Patent Application
20140330246
The embodiment of this invention is directed to an exemplary and an innovative treatment involving ‘Intra Uterine Growth Restriction’ (IUGR) of a human fetus, a long known and incurable but treatable maternal-fetoplacental pathology, resulting in significant mortality and morbidity of the fetus/neonate. The basic and clinical science research for alleviation of this elusive disease by investigators world-wide, is so far disappointing. The author inventor endeavors to disclose in this specification a simple yet clinically proved successful treatment, and it's biochemical basis. For a disease so disparagingly prevailed for decades, the said treatment disguised as simple, nevertheless demanded ramifications of it's rationale that are by no means simple, and efforts had been made to elaborate it with an infallible scientific reasoning of a compelling depth and breadth, as never done before of the subject matter. One can envision the alleviation in toto of a formidable pathology, as if the pieces of an intricate puzzle were put together. It further needed to counter the skepticism of an inquiring reader that is only viewed as truly justified. Hence the following elaboration has become arduous and rather voluminous, the author inventor also being no less skeptical and inquiring.
The definition for IUGR fetus/small for gestational age (SGA) infant is as follows—
‘Fetuses afflicted with intrauterine growth restriction (IUGR) of whatever etiology, or small for gestational age (SGA) neonates/infants of whatever etiology are those whose estimated/attained birth weights are below the tenth percentile, for the corresponding gestational age.’
The most common cause of intrauterine growth restriction (IUGR) of a human fetus is vascular in nature, resulting in placental vascular insufficiency, thus decreasing the transfer of D-glucose (the dextro-isomeric form of glucose), the prime fetal nutrient, across the placenta. Accordingly, as an interventional measure to alleviate the fetal IUGR of placental insufficiency, the specification enumerates a therapeutic measure of transamniotic isotonic D-glucose supplements in this continuation-in-part (CIP) application, however such treatment is in addition to the concommitant maternal intravenous (IV) hypertonic D-glucose supplements invariably required for the reasons that will be elaborately explained. Such interventions working in conjunction can counter the fetal hypoglycemia (defined as a sub-optimal blood glucose concentration), and also as a result the other associated metabolic derangements accountable for placental insufficiency.
The specification is directed to a novel invention encompassing many of unanticipated modalities in the specified treatment for intrauterine growth restriction (IUGR) of a human fetus, mainly due to placental insufficiency.
Chronic placental insufficiency of vascular nature decreases the placental transfer of D-glucose. The other metabolic derangements also resulting from placental insufficiency like fetal hypoxia (a demand/supply mismatch of oxygen at the tissue level having immediate or delayed adverse consequences) to mention the most menacing of the group, can be countered to a significant extent by the fetus, once hypoglycemia has been corrected, whereas there are of no fetal devices to correct it's hypoglycemia in the first place. A disclosure of providing transamniotic fetal supplements of 5% DEXTROSE (the dextroisomeric form of glucose or D-glucose) is herein described, as an additional therapeutic measure of effectively by-passing the placental impedance, after the fetus has been found to be not optimally responsive to an exhaustively implemented maternal intravenous (IV) hypertonic D-glucose supplements, thus accomplishing a means of improving fetal hypoglycemia, and consequently of the associated problems of placental insufficiency.
The Maternal Intravenous or Transamniotic D-Glucose Treatments Improve the Following Adverse Fetoplacental Consequences, Deficiencies, or of Other Effects, Resulting from Placental Vascular Insufficiency/Fetal Hypoglycemia—
1. Improvement of fetoplacental hypoxia.
2. Improvement of fetal hypercapnia (above normal blood CO2 that can have adverse effects).
3. Improvement of fetal oliguria (suboptimal urine production) and oligohydromnios (suboptimal amniotic fluid volume, corresponding to the gestational age)—with or without low fetal urea production.
4. Improvement of fetal acidosis (excess hydrogen ion concentration in the blood, leading to lowering of blood pH), including ketoacidosis.
5. Improvement of fetal Hyperlacticemia (excess of blood lactate levels) leading to lactic acidosis or else pyruvic acidosis, that need a special and separate mention apart from acidosis specified under subsection-4.
6. Improvement of fetal hypertriglyceridemia (the triglycerides circulating in the blood in a concentration above the normal standard value, or range).
7. Improved acquisition by the fetus, of major nutrients like essential/non-essential amino acids, fatty acids, and also of minerals, vitamins, and trace elements.
8. Improvement of the following, by the effect of primarily D-glucose derived-ATP mediated active transport: (a) placental L-arginine uptake for synthesis of nitric oxide responsible for fetoplacental vasodilatation and for placental vasculogenesis through angiopoietin signaling molecules, (b) placental D-lysine uptake responsible for fetal/placental neovasculogenesis—both in turn improving feto-placental hypoperfusion, hypoxia, and an over all feto-maternal exchange.
9. Improved growth and maturation of vital organs like fetal brain, for which optimal circulating D-glucose is essential, as the parent molecule/building block for the brain's phospholipids and glycolipids.
10. Improved production of ATP, the ultimate key, as the ubiquitous need for all life forms, and for all life sustaining subcellular activities, being generated by citric acid cycle, the final pathway of the predominantly prevailing glucose metabolism within the normal fetus, though it is also the ultimate meeting point for all major metabolic pathways including those of proteins and lipids.
Transamniotic fetal supplement of isotonic 5% dextrose is advisable to treat severely growth restricted fetuses after the fetoplacental priming by the prior maternal IV hypertonic D-glucose supplements, and after such associated therapeutic modalities are exhausted. The phenomenon of in-utero fetal swallowing of amniotic fluid (AF) is taken advantage of, in this additional modality of treatment.
The majority of the physiochemical improvements or consequences of improved fetal hypoglycemia accomplished through maternal IV D-glucose supplements are expected to be operative in the fetus with this therapeutic modality also, achieved by means of by-passing the afflicted placenta and directly involving the fetus, through the medium of amniotic fluid that surrounds it.
Through a Subcutaneously implanted pregnancy port (SIPP) catheter, a device specifically modified for obstetric purposes, the amniotic cavity is approached by a safe and minimally invasive surgical procedure accomplished through an extraperitoneal route for which a novel procedure is devised by the author inventor of this specification. The port is used encompassing a ‘sterile patch technique’ also devised by the author inventor to make the use completely sepsis-free so that the device is incorporated in the treatment with total confidence.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
This embodiment of invention is directed to an exemplary and novel treatment for the Intra Uterine Growth Restriction (IUGR) of a human fetus, a maternal-fetoplacental pathology, resulting in significant mortality and morbidity of the fetus/neonate. The specification encompassing a biochemical, clinical, and surgical discussion of compelling depth and of breadth, envisions total alleviation of a multi-faceted disease, for long elusive and misunderstood. Placenta, exalted to the central stage among the fetal membranes, can be considered as an indispensable structural and functional appendage of many organ systems of the fetal body that the neonate disposes off, after it's nine months of intrauterine stay. Placenta being so crucial, it's dysfunction or insufficiency often makes an indelible mark on the fetus, affecting diverse aspects of prime functions of gaseous/nutrient/substance exchange including selective transport of passing or restricting of certain maternal plasma components, and synthesizing in alliance with the fetus, optimal quantities of pregnancy hormones essential throughout gestation, that the term feto-placental unit is aptly phrased.
Chronic placental insufficiency of vascular nature decreases the placental transfer of D-glucose that was noted earlier as the most important of the fetal nutrients, resulting in on-going fetal hypoglycemia. The other metabolic derangements also resulting from placental insufficiency, like fetal hypoxia, to mention the most menacing of the group, can be countered by the fetus, once the hypoglycemia has been corrected, whereas there are of no fetal devices to correct it's hypoglycemia in the first place. A disclosure of a means of transamniotic fetal supplementation of 5% DEXTROSE infused through a novel device named Subcutaneously Implanted Pregnancy Port (SIPP) catheter, and a novel suprapubic extraperitoneal transamniotic insertion of the said SIP port-catheter are herein described, an additional therapeutic measure to resort to, for effectively by-passing the placental impedance (after the fetus had been found to be unresponsive to the exhaustive therapeutic modalities associated with the maternal intravenous hypertonic glucose supplements), thereby accomplishing a means of improving the fetal hypoglycemia.
An accelerated ‘facilitated diffusion’ can be achieved at the placental interface by therapeutically creating a transient and intermittent maternal hyperglycemia (defined as a rise in blood glucose concentration above specified normal range) by 25-50% hypertonic D-glucose bolus infusion to the mother, given over multiple times of a day, after it is confirmed that fetal IUGR is of placental vascular origin, and such maternal treatment continued until the delivery of the fetus/neonate
In a clinical setting as complex as fetal IUGR, the isolated transamniotic treatment of fetal nutrients is not deemed effective. The placenta consumes as much as 50-60% of glucose and even in diseased states it is responsible to metabolize, transform, transport, and synthesize for and in alliance with the fetus many substances that are necessary for optimal pregnancy outcome, like glucose/lactate transport, estriol synthesis—to mention a few, and in addition, accomplishes energy/ATP consuming active transport-concentration of essential nutrients and biologic substances via primarily glucose-generated ATP. Therefore, it can be evident that the transamniotic glucose supplement alone is a moot pursuit, if not done in conjunction with maternal intravenous hypertonic glucose supplements also, as such concomitant therapy nourishes the feto-placental unit, which through out pregnancy is both a structural and a functional unit. The question of the effectiveness of the transamniotic D-glucose supplements can only be answered if such needed and invariable functional accompaniments are somehow helped to be achieved by the afflicted placenta. Otherwise, intrauterine demise of the fetus happens despite an apparently adequate transamniotic D-glucose treatments. Transamniotic D-glucose supplement is the last step in the algorithmic tree (discussed in the second half of this specification) of the treatment for intrauterine fetal growth restriction, as it is also an invasive procedure. Accordingly, the physician should know in no uncertain terms why, how, and in what circumstances the transamniotic D-glucose treatment needs to be clinically pursued.
The great therapeutic effects firmly linked to the objective physiochemical principles of the D-glucose supplements and the rationale are described first under the section of THE MATERNAL INTRAVENOUS HYPERTONIC D-GLUCOSE TREATMENTS, the discussion of which is rather elaborate, and hence is not further repeated under the section THE TRANSAMNIOTIC FETAL D-GLUCOSE SUPPLEMENTS via the SIPP catheter, encountered in the last part of this specification.
At the outset, it is relevant to describe a clinical case study of successfully treating a severe case of fetal IUGR, during the years 1983-84, by the author inventor as a practicing ob/gyn in India, as it is the basis for this writing of significant depth that aided the author inventor decades later to fully comprehend what was once successfully treated, but was only incompletely understood at that time.
This single case study was with reference to a primi-gravida in her early twenties who was found to have severely growth restricted fetus in the middle of second trimester. She was well nourished and was from good socioeconomic background, and there were no obvious etiological factors, that could be accounted for the identified fetal IUGR. After monitoring the growth of the fetus by assessing fundal height (a clinical norm of fetal measure in the past) for 3-4 more weeks, it was confirmed that the uterine size was not progressing, and that the patient had severely growth restricted fetus. As the pregnancy was remote from term, and as the bed rest in left lateral position had not helped, 20% IV bolus of hypertonic D-glucose 50 cc twice daily was started, and in 2-3 weeks, an immediate catch up of fetal growth was undoubtedly observed. The patient had more frequent pre-natal follow ups, and the treatment was diligently continued, as also the patient was admirably cooperative. Nearing term, she was delivered by elective cesarean section. The baby had an apgar score of 10, and to the great delight of everybody involved, the weight was also appropriate for the gestational age (AGA). No adverse effects due to induced maternal hyperglycemia were expected, nor were any observed through-out the gestation, and the patient tolerated the treatment far beyond expectations.
The observed fetal growth restriction was undoubtedly severe, but with mere hypertonic intravenous D-glucose treatment and no other (except for standard doses of prenatal vitamins and minerals), the mother delivered an AGA baby, who obviously had caught up with standard growth curve, as though mere glucose supplements and nothing else was needed. It was evident that by mere fetal normoglycemia therapeutically restored, the fetus alleviated multitude of associated metabolic problems all by itself.
Fetal macrosomia, a known consequence of uncontrolled maternal diabetes mellitus (DM) served as a clinical model about which the therapeutic modality of this invention was/is based. Maternal hyperglycemia without super-concentration of any other element or of nutrient in the maternal blood, can accomplish accelerated fetal growth in diabetes mellitus. It exemplifies not only of an accelerated placental glucose transfer secondary to maternal hyperglycemia, but also of an accelerated fetal growth response to such accelerated transfer. Extensive research by past investigators in this subject matter proved beyond reasonable doubt that fetal growth is indeed mediated by fetal hyperglycemia, and secondary fetal hyperinsulinism (hyperinsulinemia), via the islet-cell hypertrophy of the fetal pancreas. Accordingly, this superb clinical model proved the normal placental ability of accelerated glucose transfer, and of the resultant fetal growth response by macrosomia, both together serving as the needed translational clinical outcome to the biochemical phenomenon of maternal hyperglycemia—a naturally observed consequence that might not have been otherwise available or proven, except by targeted research. However, the difference between the diabetic pregnancy and the treatment setting of IUGR in the above discussed case study—that is, the glaring prevalence/perception of fetal hypoxia, hypercarbia (hypercapnia) (as described by past researchers), and of acidosis due to placental insufficiency of IUGR is by no means over looked in this discussion
Though a single case study, it was extraordinarily impressive because of the severity of growth restriction, and the lack of confounding variables (one can be 100% sure that Indian women are never habituated to alcohol, smoking, or drugs) that clinched the diagnosis of a primary placental insufficiency of vascular origin. The present writing painstakingly endeavors to explore a physiochemical support for the specified invention—how the fetus, by mere restoring of it's normoglycemic state, or improving of a hypoglycemic state, could have possibly accomplished such an impossible feat, undoubtedly witnessed, though until this time, not completely understood.
In the diverse maternal/fetal states that cause fetal IUGR, the disease primarily afflicting placental vasculature causes more of declined functional unit area than declined unit volume of the placenta, primarily due to failed placental elaboration (into tertiary terminal villi within the normally mature placenta, over all attaining the structural intricacy of a branching tree, that it is aptly called as the ‘placental tree’). Such placental decline in the functional unit area with decrement nutritional exchange in it's interface has resulted in fetal hypoglycemia, and consequently in fetal growth restriction.
Based on the foregoing clinical model of diabetic pregnancy, and based on the fact that the D-Glucose is the prime fetal nutrient, the invention contemplates a biochemical and clinical relief, achieved by therapeutic transient hyperglycemia effectuated in the mother (an induced diabetic state) by intravenous 25-50% hypertonic D-glucose bolus infusion, 50-100 cc twice or thrice daily. By such superconcentration of glucose achieved via an IV infusion to the mother, the deprived fetal circulation receives proportionally more D-glucose, presented through the placenta in higher concentration per unit surface area/unit volume of it's yet unchangeable anatomically afflicted milieu. The function of placental glucose carrier proteins operating that far in a sub-optimal level, becomes maximal during the transient maternal hyperglycemic phase—a biochemical phenomenon explained in significant detail in the immediate subsequent sections.
Chronic vascular disease of the mother, especially pre-eclampsia was conventionally linked as the predominant cause of fetal growth restriction, mediated through placental vascular insufficiency. A wide spectrum of generalized placental vascular insufficiency (of what ever etiology) is the major pathology of concern to be alleviated through the therapeutic modality of the present invention. Normally, as pregnancy advances the uteroplacental blood flow gradually increases mainly due to spiral arterial remodeling. Very early on, due to trophoblastic invasion, the endothelium and the smooth muscle layers of the myometrial spiral vessels are replaced with loss of spiral artery vascular resistance. The lacunae further created in the syncytiotrophoblast by cytotrophoblastic invasion, and their filling with blood results in dilated pools of maternal blood sinusoids that are responsible for the shunt effect of the placenta. In an IUGR pregnancy, the trophoblastic invasion is limited to the decidual endometrium with failure of myometrial spiral arteries becoming low resistance vessels. Such placental failure in surface area elaboration and failure in sinusoidal volume/pressure effect dynamics can find relief by exceeding substrate supplements, as will be soon explained by the biochemically derived principles of transcellular substrate transport.
Although diffusion across by concentration gradient (via carrier mediated facilitated diffusion) has been described as an important method of placental transfer, the trophoblast/chorionic villus unit does exhibit enormous selectivity of transfer, maintaining different concentrations of a variety of metabolites on the two sides of the villus (via ATP/energy expending, carrier mediated ‘active transport’, a placental concentrating process against a concentration gradient). It was deduced by the observation that the concentrations of a number of substances that have not been synthesized by the fetus are found several times higher in the fetal blood than in the maternal blood. In contrast, the transfer across the placenta of D-glucose, the prime fetal substrate central to this discussion, is accomplished by carrier mediated, stereospecific, and non-concentrating no-energy expending process that can be saturated, said process termed as ‘facilitated diffusion’.
The Michaelis-Menten equation is an expression of the relation of substrate concentration and the resultant rate of an enzyme/hormone/a cell membrane-cytosol located substrate-carrier mediated chemical reaction, either by active transport or by facilitated diffusion.
(In what follows, the D-glucose needs to be considered as the ‘substrate’, and the GLUT-1 & GLUT-3 as it's substrate-carriers, located in the placental membrane. The enzyme/hormone involvement is also emphasized, the hormone relevant in this context being insulin)
In a typical chemical reaction involving an enzyme/hormone, or in a membrane transport mediated by a substrate-carrier (involving either active transport or facilitated diffusion), if the concentration of the substance/substrate (S) is increased while all other factors are kept constant, the measured initial velocity v1 (the velocity attained when very little substance/substrate (S) has reacted with it's enzyme/hormone/carrier) increases until it reaches a maximum attainable velocity (Vmax) and can increase no further, even with further increase of the substance/substrate (S), when the enzyme/hormone or carrier is said to be saturated.
If (S) is the substance/substrate concentration, the ‘Michaelis constant’ (Km) is the substance/substrate concentration at which the initial velocity v1 is half of the maximal attainable velocity (Vmax/2) at a particular concentration of the enzyme or carrier involved/available in a reaction. When (S) is approximately equal to Km value, v1 is very responsive to changes in (S), and the enzyme/carrier is working at half maximal efficiency. When the substance/substrate concentration (S) far exceeds the Km value, the initial velocity v1 is maximal (Vmax). Furthermore, in this situation the reaction's maximal velocity Vmax is almost instantaneous, as all the available enzyme/carriers are able to bind to the exceeding amounts of substance/substrate (S) all at once, and no further binding possible.
Machaelis-Menten expression shows in mathematical terms the relationship between the attained initial reaction velocity v1, and the reacting substrate/substance concentration (S), as depicted below—
Under physiological D-glucose concentrations of the maternal blood, the placental carrier transporters for glucose were found to be far in excess, with a reserve able to be accommodating further addition of an exceeding amount of D-glucose presented at the placental interface. This implies that the carriers are always functioning in suboptimal manner under physiological concentrations. Insulin heightens the recruitment of such carrier molecules from the intracellular pool. At times of placental compromise, the unit surface area of placental terminal villi are still transporting glucose in a manner similar to unaffected placental villi. However, the underlying problem in IUGR is the markedly reduced total surface area/volume of the terminal villi secondary to failed placental elaboration, and as a result markedly diminished number of terminal villi that diminish the over-all glucose transport through the available total surface area of the placenta, per unit time. It implies, therapeutic maternal hyperglycemia with increased substrate/glucose (S) concentration can recruit more of carriers per unit surface area of the villi, that is, the carrier molecules available in surplus, now function at maximum rate to transport far exceeding amounts of glucose across the yet unchanged placental interface in unit time, as increased substance/substrate (S) concentration not only increases v1 to Vmax (a maximal attainable speed) of each transport carrier, but also increases the number of such maximally functioning carriers in the unit placental surface area, now recruited in higher number (as a result of increased insulin levels proportional to increased D-glucose), due to the demand of increased substance/substrate (glucose) availability in unit time. That is, the heighted D-glucose facilitated diffusion following maternal hypertonic D-glucose supplement is the multiplied product of attained Vmax×the maximally recruited carriers all working at Vmax, the Vmax being instantaneous in time. The said Vmax is highly significant in IUGR with markedly diminished diastolic filling of the umbilical vessels, and only the shorter systolic time (of each cardiac cycle) providing for a better or any placental exchange.
Failure in the development of terminal villi and their capillaries whose contribution for placental maternal-fetal exchange increases exponentially during 31-36 weeks of gestation, could account for fetal IUGR in significant number of pregnancies so afflicted. This was found to be associated with reduced umbilical artery end diastolic flow, which is otherwise increased in normal pregnancy. Histometric support of this hypothesis is provided by the observations of reduced terminal villi volumes as well as reduced surface areas of the placentae of the IUGR fetuses (Tesdale F, 1984. Failure in the ‘fall of maternal peripheral vascular resistance’ usually by 16%, observed throughout in a normal pregnancy, can also be expected in this context.
The
Effects of Placental Insufficiency Other than Hypoglycemia—
Fetal hypoxia, hypercapnia, lactic acidosis, and impaired feto-maternal exchange across the placenta are the biochemical consequences for long conventionally linked to the primarily declined placental function, yet this specification convincingly proves by available objective data that the therapeutic intervention of IV hypertonic glucose supplement in and by itself effectively relieves the said biochemical consequences. Such observation/deduction conforming to the needed ‘as a whole inquiry’ carries enormous significance in dispelling the possible skepticism that—glucose supplement might relieve fetal hypoglycemia, but the other invariable associations of placental insufficiency such as hypoxia and the like are still detrimental to the fetal well-being, and hence the proposed treatment is of no consequence.’
The D-Glucose, the fittest fetal fuel—
There are operational mechanisms in pregnancy to minimize glucose utilization by the mother, thereby making it available to the fetus, glucose being it's prime nutrient, intended by nature. Human Placental Lactogen (HPL), a pregnancy hormone secreted by the placenta, and normally present in the mother but not in the fetus, is believed to be blocking the peripheral uptake and utilization of D-glucose by maternal tissues, while also promoting the mobilization and the utilization of free fatty acids (FFA) by the mother for energy requirements. Fats and proteins are also transported across the placenta, but they play a major role only in anabolic function of rapid tissue accretion needed for optimal fetal growth, or for targeted bodily functions, but not for the catabolic energy-yielding purposes within the fetus. The scientific rationale why D-glucose is the chosen fetal fuel for the therapy, and not any other major nutrients acclaimed as equal (the proteins), or superior (the lipids) in ‘food caloric value’ focuses on the nature's rationale itself (and hence this invention's) for it's selection as the fittest. Such biochemical derivation is very relevant to this discussion, as other supplements if promoted as prime fetal nutrients (at the expense of glucose) are clearly detrimental, and may not be considered as potential fetal energy/ATP sources.
The major compromise that has direct bearing in fetal demise/deterioration in the setting of fetal IUGR is undoubtedly linked to fetal hypoglycemia and fetal hypoxia. GLUCOSE because of it's dominant function in the ultimate catabolic oxidation via the ‘citric acid cycle’ is pivotal in generating ATP, the source of life and energy. Though OXYGEN (O2) is breathed-in by all living organisms, and taken up by the fetus from the maternal source, ultimately it is the cellular respiration and ‘oxidative phosphorylation’ via molecular oxygen within the mitochondria, the ‘power house’ organelles of the cell, that are ultimately responsible for generating ATP, via the maneuvers of the D-glucose mediated ‘citric acid cycle’.
Accordingly, what happens at large at the organ level is ultimately reflected at the cellular and biochemical level and vice versa, and understanding such micro-functions of cell organelles as the ultimate ATP generators to sustain life is the only clue to explore or search for any convincing relief to be sought for the significant fetal deficits such as hypoglycemia and hypoxia, while the placental pathology itself may not be alleviated. It necessitates the in-depth biochemical discussion of the major (the carbohydrate, lipid, and protein), and some minor fetal metabolic pathways invariable for discovering what is yet undiscovered, or for dispelling legitimate concerns that may not by other means be explained, nor over ruled. The compelling motivation for such diligent exploration is the author inventor's successful case study itself that proved that there is something intriguing that is yet to be explored and found. What is found is truly intriguing as was thought (though some are universally known biochemical/biophysical facts under different context), and is herein elaborated in the following sections.
The carbohydrates, characterized by a basic compact structural formula C(n) H(n) O(n) (the carbon, hydrogen, and oxygen being present in varying number n) are the aldehyde or ketone derivatives of polyhydric alcohols, existing either as isomeric straight chains or as stable 5 carbon (furanose) or 6 carbon (pyranose) ring structures. They are universally distributed in all living forms. In plants they are synthesized as starch by the photosynthetic reaction between CO2 (carbon dioxide) and H2O (water), and animals ultimately derive the required carbohydrates primarily from plant sources, only insignificant amounts being synthesized in the animal body from the proteins and the lipids. The most interesting and foremost member of the class, the glucose, a hexose sugar (one having 6 carbon atoms) is represented in a compact chemical formula as C6H12O6, and the H+ and O2 present in the same ratio as that of water molecule may be noted, as the carbohydrates are water-rich substrates, a property responsible for their bulk (compared to the fats/lipids that are water-desiccated during their synthesis from the parent carbohydrates, as can be observed later in this discussion, and hence are acclaimed to carry higher energy in the same unit weight), and such structure representing the hydrogen-oxygen ratio of water molecule can also be noted in the triose, tetrose, and pentose sugars.
The Carbohydrates are Classified as—
1. Monosaccharides—they are carbohydrates that can not be further reduced to simpler forms. They comprise of trioses (ex.—dihydroxyacetone, the important intermediate of glycolysis), tetroses, pentoses (ex—the ribose sugars of DNA and RNA), and of hexoses (ex—glucose, fructose, and galactose), each containing 3, 4, 5 or of 6 carbon units respectively. All dietary complex carbohydrates are broken down, and absorbed into the body in simpler monosaccharide form, such as glucose.
2. Disaccharides—they are made of 2 monosaccharide units (ex—sucrose and maltose).
3. Polysaccharides—they are made of more than 10 monosaccharide units (ex—starches, dextrins).
The major pathways of carbohydrate metabolism having substantive clinical and biochemical significance, and relevant to this discussion, are—
Glycolysis, the initiating pathway for the D-glucose metabolism, occurs in the cytosol (the cytoplasm) of the cell, and is unique in that it can occur either aerobically or anaerobically. It is also the main initiating metabolic pathway of fructose, galactose, and also of the other carbohydrates derived from the diet. It is schematically shown in the
Evidently, 2 molecules of pyruvate (29) are produced from 1 molecule of glucose (1) at the end of glycolysis in the cytosol, both to enter citric acid cycle (98) under aerobic conditions. The alternate pathway of anaerobic glycolysis (involving lactate dehydrogenase) prevailing in hypoxic conditions, and depicted on the left of the step-6 (catalyzed by the enzyme glyceraldehyde 3-phosphate dehydrogenase) of glycolysis, will be detailed in a later section.
The Formation of Acetyl-CoA from Pyruvate—
The pyruvate formed in the cytosol is transported into the mitochondrion. In the inner mitochondrial membrane, the pyruvate is oxidatively decorboxylated to acetyl-CoA (acetyl Co-enzyme A) (97) by a multi-enzyme complex, the ‘pyruvate dehydrogenase complex’. One molecule of CO2 is also generated in this step. This reaction is irreversible, and requires the presence of thiamine (the vitamin B1), FAD (the flavin adenine dinucleotide, or the flavoprotein), NAD+, and lipoamide. It is clinically relevant to note that in states of thiamine deficiency pyruvate accumulates causing pyruvic acidosis, with the symptoms of beri-beri. The requirement of thiamine is proportional to the carbohydrate intake. In this reaction, NAD+ is reduced to NADH+H+, which in turn transfers reducing equivalents (2H+ or protons) to the ‘respiratory chain’ under aerobic conditions, producing 6 ATP from 2 pyruvate molecules derived from 1 molecule of glucose. The formation of acetyl-CoA (97) and CO2, from the oxidation of pyruvate (29) within the mitochondria, and the acetyl-CoA (97) so generated entering the citric acid cycle (98) are also illustrated in the
The Krebs citric acid cycle or the tricarboxylic acid cycle (
It can be noted that during combustion of 1 molecule of D-glucose (86), a total of 6CO2 molecules are liberated: (a) 2 CO2 during the formation of 2 acetyl-CoA (83) molecules from 2 pyruvate (85) molecules, and (b) 4 CO2 during the citric acid cycle (also involving 2 cycles).
The outlines of the scheme of oxidative phosphorylation are illustrated in the
Oxidation is the addition of oxygen to, or removal of hydrogen from an element or compound. Essentially, it is removal of electrons. Reduction is the addition of hydrogen to or removal of oxygen from an element or compound. Essentially, it is gain of electrons. Accordingly, many reactions of biologic oxidation can take place via dehydrogenation (through dehydrogenase enzyme complexes that can not use oxygen as a hydrogen acceptor) even without the participation of molecular oxygen.
In the aerobic organisms, during the oxidative phosphorylation that takes place inside the respiratory chain (33) of the mitochondria, the oxidation is tightly coupled to phosphorylation (Mayes P A) to generate the high energy intermediate, the ATP. Most of such energy to be liberated during the oxidation (the catabolism) of carbohydrates, proteins, and of fats is made available within the ‘respiratory chain’ of the mitochondrial matrix as reducing equivalents (2H+ or the electrons of NADH+H+ or FADH2) that are collected and are transported for their final interaction with molecular oxygen (½ O2) (81) to form water (H2O) (77). The respiratory chain (33) contains a number of redox carriers, arranged in sequence as—the NAD+ linked dehydrogenase, the flavoprotein, the ubiquinone, and the ‘cytochromes’ that are cytochrome b (cyt b), cytochrome c1 (cyt c1), cytochrome c (cyt c), and cytochrome aa3 (cyt aa3), arranged in that order. Each of the respiratory chain (33) complexes act as a ‘proton pump’. According to Mitchell's chemiosmotic theory, through the process of oxidation in the respiratory chain, energy is derived that is used for the translocation of protons (H+) to the exterior of mitochondrial inner membrane. The mitochondrial membrane being generally impermeable to ions, especially protons, (the FADH2) generated in the reaction catalyzed by succinate dehydrogenase (41) produces only 2 ATP. When either 1 NADH+H+ or 1 FADH2 participates in the oxidative phosphorylation, ½O2 (81) is utilized to interact with the reducing equivalent (the 2H+) to form water (H2O) (77), and also simultaneously 3 or 2 ATP respectively.
A total of 6O2 is required to completely oxidize 1 molecule of D-glucose to produce 38 ATP, as can be observed in the following table-1. This factual knowledge is important in understanding the ‘best economics’ of glucose as the fetal fuel to generate ATP, and the frugality of this hexose sugar is never found during the catabolic use of proteins or of lipids, in terms of oxygen expended during similar gain of ATP for the fetus deemed to thrive in relatively hypoxic states in utero. The rather complicated process of oxidative phosphorylation is only briefly outlined here, the in-depth enumeration of which is beyond the scope of this discussion, but can be found in any standard text book of biochemistry.
Under anaerobic conditions (111), the end product of glycolysis is lactate (113) that is derived from pyruvate (29). The scheme of anaerobiosis or anaerobic glycolysis (111) is also shown in
The inner mitochondrial transporter system also has phosphate transporter (that allows the transport of inorganic phosphate that passes readily as H2PO4− ion) that exists in combination with adenine nucleotide (the ADP and ATP) transporter. In the so called process of ‘oxidative phosphorylation’ the molecular oxygen (81) derived from the respiration of the organism in fact makes no structural contribution to ATP, and actually forms H2O (77) (in the final chemical reaction of ‘oxidation’ within the respiratory chain, 33), combining with 2H+ of NADH+H+ or FADH2. The phosphate group (PO4−) added to ADP is wholly derived from H2PO4− (the dihydrogen phosphate ion entering the inner mitochondrial membrane through it's transporter). It can be shown in a simplified schematic form, as below—
The merging into the Krebs citric acid cycle, of proteins (amino acids) (of groups 43, 47, 53, 55, 61, and 65) and lipids (the free fatty acids) (49) as acetyl-CoA (51), or as the citric acid cycle (31) intermediates for their final catabolic disposal to generate substantial amounts of ATP, is also shown in the
2 NADH+H+ (15) of step-6 of glycolysis, precluded from being used in the mitochondrial oxidative phosphorylation (115) of the respiratory chain (shown on the right side of the step catalyzed by glyceraldehyde 3-phosphate dehydrogenase) to otherwise produce an additional 6 ATP (3 ATP from 1 NADH+H+). It may be understood that only one of the alternate pathways, either the one depicted in the left (the anaerobic glycolysis), or the one depicted on the right (the aerobic glycolysis) of the step-6 catalyzed by glyceraldehyde 3-phosphate dehydrogenase in
With the availability of glucose (1), though glycolysis can be continued indefinitely even in hypoxic/anoxic conditions, it is not without adverse effects on the fetus neonate, as it can lead to lactic acidemia with the consumption of fetal base reserves, a situation only rescued by oxygen.
The Malate shuttle (76) (illustrated in
It can be noted that the steps of forming α-ketoglutarate (44) from oxaloacetate (38) via malate shuttle (76) are very different from the steps involved for the formation of the same via the citric acid cycle (
The pentose phosphate path way or HMP shunt is a specialized route of glucose metabolism, as it mainly has anabolic significance, and accordingly does not generate ATP. It has two major synthetic functions—
1. Formation (from NADP+) of NADPH+H+ (the phosphorylated form of nicotinic acid adenine dinucleotide and the hydrogen ions) that participates as a hydrogen donor during the synthesis of free fatty acids (FFA), and of steroids.
2. Formation of D-riboses, the pentose sugars vital for the synthesis of nucleotides, and the nucleic acids, the DNA and the RNA (deoxyribonucleic acid and the ribonucleic acid).
The pentose phosphate pathway or the HMP shunt (HMPS) is a more complex path way than glycolysis. 3 molecules of glucose give rise to 3 molecules of ribose sugars, and it can be noted also that 3 molecules of CO2 are produced in this process. The NADP+ (the phosphorylated form of nicotinic acid adenine dinucleotide) is used in the path way as the hydrogen acceptor. The process is extra-mitochondrial and is more active in tissues predominantly engaged in the synthesis of free fatty acids, and of steroids. No oxygen is used in the pentose phosphate path way, as obviously the reducing equivalents (the 2H+) acquired by the coenzyme NADP+ via the path way are meant to be used for the anabolic syntheses of free fatty acids, steroids etc.
The significance of glucose as the predominant fetal fuel for the reasons of it's high ATP yield, and accordingly as the chosen fetal nutritional supplement in the treatment modalities of this invention can be best appreciated only in the light of the discussion of the lipid and of the protein metabolic path ways within the fetal body, the latter path way most surprisingly expending oxygen/ATP in a rather extravagant manner even before it's end products gaining some similar number of ATP as the other merging metabolic end products, via the ultimate steps of the landmark meeting point, the citric acid cycle. This knowledge, acquired in the light of biochemical and mathematical evaluations/equations is needed for an understanding that is reliable and objective.
LIPIDS in their SIMPLE form are heterogeneous group of compounds that are essentially esters of fatty acids with various alcohols, the fatty acid straight chain in natural form existing either as a saturated or unsaturated aliphatic carboxylic acid.
The lipids as a class have the common property of being insoluble in water, and soluble in solvents like chloroform and ether. They comprise the major constituents of human diet, and are significant for their high energy value per unit volume/weight, and accordingly, are efficient energy store-houses of the body, to be used on demand. They are important for their containment of fat soluble vitamins also. The lipids comprise the following major classes:
Simple lipids,
Complex lipids,
Precursor or derived lipids, and
Neutral lipids.
1. Simple lipids—these are esters of saturated or unsaturated fatty acids with various alcohols (ex—glycerol, sphigosine). The acetic acid, palmitic acid, stearic acid etc. are the examples of saturated fatty acids, whereas linoleic, linolenic, arachidonic, and ω3 hexaenoic acids are examples of unsaturated fatty acids. Palmitic acid, and ω3 hexaenoic acids (that ultimately form complex phospholipids in the brain starting from chain elongation of palmitic acid) are synthesized in humans, whereas the linoleic, linolenic, and the arachidonic acids are essential fatty acids that are to be primarily derived from food, either of plant or of animal sources.
2. Complex lipids—these are esters of fatty acids and alcohol, also containing additional groups like a phosphoric acid residue, a carbohydrate, or a protein, as in the following groups—
This discussion is important as the lipogenesis is an integral part of the developing brain (and the thermoregulatory subcutaneous adipose tissue), and it is critical to know how best this vital organ can be spared from growth restriction by obviating the need for otherwise excessive amount of molecular oxygen. As the 16 carbon atom fatty acid, the palmitic acid is the predominantly synthesized fatty acid in the fetus (that can be further elongated to a fatty acid with 24 carbon atoms chain in certain tissues, as in the brain), it is chosen as the prototype example for the present discussion of fetal fatty acid biosynthesis.
It was noted in the foregoing discussion of the carbohydrate metabolism (under subsection-2 of the citric acid cycle) that acetyl-CoA is an intermediate that is formed from pyruvate after it's entry into the mitochondria, and that it is the building block of the fatty acids. The lipid anabolic process starts at the outset as the glucose catabolic process (the glycolysis) that expends O2, and also generates ATP in that process.
It has to be noted that though acetyl-CoA, the building block of the free fatty acids is generated within the mitochondria from pyruvate, the synthesis of palmitic acid (and all fatty acids) is extra-mitochondrial (cytosolic).
The Biosynthesis of the Free Fatty Acids (FFA), with Palmitic Acid Chosen as the Prototype for Discussion, is as Below—
1. Acetyl-CoA (the building block of fatty acids) formed in the mitochondria can not penetrate the mitochondrial barrier to enter the cytosol, and hence has to form citrate via the citric acid cycle, and the citrate so generated can get out into the cytosol (in exchange with malate) through the mitochondrially located citrate (or the tricarboxylate) transporter.
2. Citrate, within the cytosol, is cleaved to acetyl-CoA and oxaloacetate (
3. Acetyl-CoA in the cytosol is carboxylated to melonyl-CoA, in the presence of ATP by acetyl-CoA carboxylase. This reaction requires HCO3− (as the source of CO2), biotin, a B-complex factor and manganese.
4. Melonyl-CoA condenses with one more acetyl unit, when CO2 added in the previous step is liberated. As this reaction takes place while the reacting molecules are still attached to the surface of an enzyme complex, the fatty acid synthase multienzyme complex (E), it can be written as—
The product of this reaction is an enzyme bound acid with 4 carbon atoms, with a keto group (the CO group, with a double bond) being located in β position. The carbon atoms are numbered from carboxyl (CO) carbon (the number 1). The adjacent carbon atoms, numbered 2, 3, and 4 are also referred as α, β, and γ carbon atoms. The fatty acid group after it is evolved from the basic acetic group of the first member of the fatty acid series, the acetic acid (CH3-COOH), is referred to as an acyl group.
5. Reduction of β-keto group of aceto acetyl enzyme (3-keto acyl enzyme) by 2 NADPH+H+ catalyzed by 3-keto acyl reductase, gives rise to an enzyme bound 4-carbon acyl enzyme or 4 carbon butyryl enzyme which is a saturated enzyme bound fatty acid (butyric acid is the third member of the fatty acid series, containing 4 carbon atoms).
NADPH+H+ is readily available as the by-product of HMP shunt that is cytosolic also. HMP shunt (HMPS) is highly active in most of the fetal tissues, including the placenta, due to the function through the shunt, of production of ribose sugars (needed for the DNA and RNA, essential for fetal/placental cell replication). The carbohydrate oxidative reactions of HMPS reduces NADP+ to NADPH+H+ that is the main source of hydrogen required for the reductive synthesis of fatty acids, as in case of palmitic acid, a total of 28H+ ions are added through it's biosynthesis, via the NADPH+H+.
6. In a reaction similar to reaction 4 above, another melonyl unit is added to the carboxyl end of the 4 carbon butyryl enzyme to generate a 6 carbon 3-ketoacyl enzyme that is still enzyme bound. One molecule of CO2 is also liberated in the process in a similar manner.
The product of the reaction can be named as 3-keto caproyl enzyme (caproic acid is the fifth member of fatty acid series containing 6 carbon units).
7. The new 6 carbon 3-keto acyl enzyme or 3-keto capryol enzyme is then reduced to the corresponding 6 carbon saturated fatty acid, the 6 carbon acyl enzyme or caproyl enzyme, by 2 NADPH+H+ through the enzyme 3-ketoacyl reductase in a reaction similar to reaction 5 above (also involving similarly named enzyme), as follows—
8. In the next step there will be again addition of melonyl unit to elongate the 6 carbon acyl enzyme to 8 carbon 3-keto acyl enzyme. Such repetitive and alternating additions of melonyl enzyme and then the 2H+ of NADPH+H+ to first produce a 3-keto acyl enzyme, and then a corresponding saturated fatty acid enzyme respectively, result in the production of 16 carbon Palmitic acid through chain elongation by 2-carbon addition, followed by 2H+ addition each time. The fatty acid (the palmitic acid) so formed is still enzyme bound, but splits off at the end, as free 16 carbon palmitic acid: CH3—(CH2)14—COOH. The sequence can be stated as: the addition of 2 carbon units by melonyl-CoA to the carboxyl end of the fatty acid chain with formation also of a 3 keto group, followed by reduction of the 3 keto group with 2H+ of 2 NADPH+H+.
The summated equation of the biosynthesis of palmitic acid from acetyl-CoA and the melonyl-CoA can be shown as follows—
It can be understood that a total of 8 acetyl-CoA units, or 4 glucose molecules are required in the biosynthesis of 1 molecule of palmitic acid.
Coming back to reactions 1 and 2 of palmitic acid synthesis, it was stated that the citrate (99) gets out of mitochondria into the cytosol, and within the cytosol, it is cleaved to acetyl-CoA (105) and oxaloacetate (107) (
Fatty acid catabolism by oxidation, otherwise called as β-oxidation, like the citric acid cycle, is mitochondrial, and utilizes NAD+ and FAD as coenzymes, and aerobically generates ATP via the mitochondrial respiratory chain. Compared to D-glucose oxidation via glycolysis, fatty acid oxidation is a more oxygen consuming process, in terms of similar ATP gain. The end products of β-oxidation of fatty acids are multiple units of acetyl-CoA, destined to enter citric acid cycle to be subsequently catabolized in a similar manner as the acetyl-CoA molecule derived from glucose itself (or from any other source that merges into the cycle). Just as the β carbon unit (3 carbon unit from the carboxyl end) of the growing fatty acid chain was reduced during fatty acid synthesis as described in the foregoing section, the β carbon unit of the fatty acid chain is oxidized in successive steps during this process, to cleave an acetyl-CoA unit each time. The fatty acids by their high yield of acetyl CoA, are enormous sources of energy compared to similar unit volume or weight of protein or carbohydrate, as virtually fatty acid synthesis is a ‘desiccative process’ (of the parent glucose molecule) that eliminates water as shown in reactions 5 and 7 of it's synthesis from the water-rich carbohydrate precursors. Make note of the addition of 1 molecule of water (that was earlier lost in the synthesis) in reaction-3 below, as each molecule of acetyl CoA is cleaved. The β-oxidation of palmitic acid, the chosen prototype of the group, is described in the following discussion.
1. The fatty acid in the cytosol is first activated to an active fatty acid or acyl-CoA (or the palmityl-CoA) by acyl-CoA synthetase located in the outer mitochondrial membrane—a reaction that requires ATP, which is reduced to AMP and PPi.
2. Within the mitochondrial matrix two carbon units at a time are cleaved from the acyl-CoA molecule, starting at the carboxyl end. In the following reactions the compact formula of the 16 carbon unit palmitic acid, CH3—(CH2)14—COOH is shown as:
CH3—(CH2)12—CH2—CH2—COOH
with two of it's CH2 groups shown as discrete α and β carbon groups, to high-light the reactions involving these groups.
3. The first step within the mitochondria is the oxidative removal of two hydrogen atoms from the 2 (α) and 3 (β) carbon units of the acyl-CoA through the enzymatic action of acyl-CoA dehydrogenase in the presence of the coenzymes FAD (that is reduced to FADH2), and NAD+ (that is reduced to NADH+H+), with also an addition of 1 molecule of water. The oxidative phosphorylation of FADH2 via the respiratory chain yields 2 ATP, whereas that of NADH+H+ yields 3 ATP (with a total gain of 5 ATP), each reduced co-enzyme using ½O2 (and a total of 1O2) in the process. The reaction cleaves 1 molecule of acetyl-CoA from the fatty acid chain.
It has to be noted that in the below specified equation, it is the highlighted (in bold print) third or the β-carbon unit of the 16 carbon acyl-CoA that is oxidized by the oxygen of the water molecule (the β-oxidation) in a series of steps. To start with, the α and β groups that are the 2 and 3 carbon units (CH2—CH2) respectively, are oxidized to CH═CH by FAD. Then in a reaction involving H2O, NAD+ and CoA—SH, they are transformed to CO—CH3 following which the 1 and 2 carbon units of the fatty acid chain (the 1 carbon unit remaining as carboxyl carbon CO, but the second α-carbon unit CH2 has been changed earliest to CH3) are cleaved to form acetyl-CoA, while the β-carbon will be forming the carboxyl carbon CO of the new fatty acid chain. The FADH2 and NADH+H+ are formed at the end of these reactions. The summated overall reaction is as shown below—
The cleavage of the subsequent molecules of acetyl-CoA from the remaining 14 carbon unit fatty acid chain (the acyl-CoA) can be shown as in the following equation. In this equation, the compact formula of the 14 carbon atom acyl-CoA of above reaction is again shown with 2 of it's CH2 groups as discrete α and β groups, to clarify the chemical action involved in these groups.
The oxidative process involving the α- and the β-carbon units (the 2 and 3 carbon units) are similar, as was summated for the foregoing overall reaction.
In the reaction described above, one more molecule of water is consumed, and the β carbon unit of the fatty acid becomes the carboxyl carbon unit of the new acid, containing 12 carbon units, while the second molecule of acetyl-CoA is cleaved. Repetition of the sequence results in the cleavage of the whole fatty acid chain into units of acetyl-CoA. In the case of palmitic acid, the sequence is repeated 7 times, to yield 8 molecules of acetyl-CoA, and 35 ATP (7×5), with the consumption of 7O2 and 2 high energy phosphates, the latter used for the initial activation of fatty acid. There is a net result of 33 ATP during the complete catabolic β-oxidation of palmitic acid to 8 units of acetyl-CoA.
The Comparison of Oxygen Consumption Vs. ATP Yield, During Glycolysis and β-Oxidation—
The consumption of oxygen, and yield of ATP during β oxidation can be compared to glycolysis (when 4 glucose molecules are spent), for similar yield of 8 acetyl-CoA, as shown below—
As per the above, via glycolysis, 1O2 produces 7 ATP, whereas via beta oxidation only 4.7 ATP are produced. That is, via glycolysis, the 7 ATP generated consuming 1O2, are generating 2.3 more ATP compared to beta oxidation, when similar amount of oxygen is expended. It is significant that per 100 ATP so produced, the glycolytic pathway of D-glucose is generating 32. 85 more ATP, or the ATP yield via glycolysis is 32. 85% more, compared to beta oxidation. Evidently, 32.85% (⅓rd of requirements) is also the equivalent amount of O2 salvage, or reduced oxygen requirement via the glycolytic path way of D-glucose.
Starting as the size of a single cell ovum or a fertilized egg, and attaining in-utero of the size of a full term fetus of 3.5 kg or more in 280 days, nothing in nature and in health can surpass the growth potential of the developing fetus. For such unsurpassed growth, Oxygen is as valuable fetal currency as the food sources it can consume in a relatively hypoxic uterine habitat. With 32.85% excess of energy (ATP) provisions (or 32.85% of reduced O2 expenditure, compared to the ‘most superior lipids’ of the food group) in terms of food energy yield vs. oxygen spent, glucose is but the most fitting fuel of the fetus during it's in-utero stay through ten lunar months.
Why Less Oxygen is Needed when Carbohydrates are Metabolized—
It had been discussed that during glycolysis-citric acid cycle, when 1 molecule of D-glucose is metabolized, 6O2 are used, and also 6CO2 are produced. It makes the RQ (the respiratory quotient) of D-glucose/carbohydrates as 1. RQ is the ratio of the number of CO2 molecules produced, and the number of O2 molecules consumed (CO2/O2) during a metabolic process in an unit time. When fats are metabolized the RQ falls to 0.7. It is because of the fact that in the carbohydrate molecule there is enough oxygen present to oxidize the hydrogen present within the molecule to produce water (H2O), and hence oxygen from extrinsic sources is needed only to oxidize the carbon (to produce CO2) present within the molecule. It was earlier noted how all the carbohydrates—the trioses, tetroses, pentoses, and the hexoses contain H+ and O2 in the same ratio as that of the water molecule (it is high-lighted in the compact formula of glucose below).
When fat is combusted the oxygen present within is not sufficient so that extrinsic oxygen is needed to oxidize both it's hydrogen and carbon atoms (Chatterjee CC).
The RQ is exemplified below as in the metabolic break down of glucose, the prototype carbohydrate, and tristearin (a triglyceride composed of 1 molecule of glycerol, and 3 of stearic acid) taken as the prototype lipid.
C6H12O6+6O2→6CO2+6H2O; RQ: 6CO2/6O2=1 Glucose
2C3H5(C18H35O2)3+163O2→114CO2+110H2O; RQ: 114CO2/163O2=0.7 Tristearin
As can be seen in the above equations, 6 molecules of O2 are used in the combustion of glucose to produce 6CO2, and the 6H2O molecules liberated were already present within the glucose molecule as high-lighted, whereas for the combustion of 2 molecules of tristearin, 163 molecules of O2 are required to oxidize 220H+ to produce 110H2O, and also to oxidize 114 carbon atoms to produce 114 CO2, as the O2 present within the 2 molecules are only 12.
The above discussion of fatty acid beta oxidation clarifies that when fats are utilized as the source of energy, the acetyl-CoA are generated in enormous numbers. They are destined to merge into citric acid cycle for their further catabolic disposal. In times of diminished glucose availability as in IUGR, due to lack of sufficient amounts of oxaloacetate, that has to be derived from glucose, acetyl-CoA can not merge into citric acid cycle. It's further fate is to form ketone bodies—the acetoacetic acid, β hydroxybutyric acid, and acetone. These are strong acids that are responsible for ketoacidosis. Their disposal is an oxygen consuming path way that further saturates fetal oxidative machinery.
In the fetal hypoglycemic states with proportional hypoinsulinemia, the fat depots are mobilized by the unopposed hormonal lypolytic effects. With the resultant acetyl-CoA in enormous amounts, and fat utilization via beta oxidation, not only 33% of excess oxygen is used, but also more is required to dispose of ketone bodies, and alleviate acidosis. There is sufficient evidence in the literature to indicate that in the healthy fetus of normoglycemic status, all the lipid components crossing the placenta will be used for anabolic purposes and invariable bodily functions, and rarely for catabolic purposes.
PROTEINS are complex and generally high molecular weight organic compounds made of AMINO ACIDS that are distinguished by the presence of an amine group (—NH2) containing a nitrogenous base, a carboxylic acid group (—COOH), and an aliphatic or aromatic side chain of variable structure specific to each of the amino acid.
The Aliphatic group in a protein signifies an open straight chain, whereas an aromatic group is a closed benzene-like ring structure, as in proline, tyrosine, histidine, phenylalanine, and tryptophan. The so called nutritionally essential amino acids (10 in number) must be only derived from the diet, and the rest, the non-essential amino acids (12 in number), by virtue of their short biosynthetic pathways, can be synthesized within the body. Despite the nomenclature, all twenty two of the ‘proteinogenic’ amino acids are essential for optimal health, in all stages through life. Though glucose is considered as universal fetal fuel, there is uncompromised need for all amino acids throughout the intrauterine life—not only as the structural elements of the muscle bulk of the developing fetus, but also as the integral micro-components that range from enzymes/hormones/neurotransmitters to nucleic acids that make up the essential architecture of DNA and RNA.
Proteins/amino acids, unlike D-glucose, are extravagant members in terms of expending oxygen or ATP throughout their metabolic processes, including processes involved in disposal of some of their end products. Indeed their oxygen or ATP requirements are even more than their above discussed lipid counterparts, and their use as energy source as in IUGR is undoubtedly coupled with enormous ATP/oxygen wastage, though it may not be the case in an optimally growing fetus. Proteins are the unique members that generate major excretory products—the ammonia, uric acid, CO2, and the creatinine, that all need immediate and ongoing disposal, whereas CO2 is the only excretory product culminating from the break-down of the carbohydrates and of the fats. For the disposal of the toxic by-product of protein break down i.e. the ammonia (NH3+, derived from the amino group), significant energy needs to be expended for the synthesis in the liver, of relatively non-toxic urea, from the ammonium radical and the CO2.
The metabolic energy yielding end products of protein break-down comprise of acetyl-CoA, or else the intermediates of the path ways of glycolysis-citric acid cycle (ex—pyruvate, oxaloacetate, succinyl-CoA, α-ketoglutarate etc), wherein they merge for their ultimate catabolic disposal, to produce ATP via the respiratory chain. Similar to beta oxidation of lipids, they also produce some ATP (through the NADH+H+) during their catabolic break down before merging into the citric acid cycle, but through the metabolic steps and through the ultimate disposal of their excretory products, there is surprising net loss of ATP for an IUGR fetus (due mostly for the ammonia disposal as urea, in some cases two or more of ammonia molecules derived from multiple amine-groups of an amino acid), a situation worse than what was encountered during beta oxidation of lipids, that was already critically viewed by objective mathematical analysis as far inferior in comparison with the unsurpassed yield via the pathways of glycolysis, in terms of the ATP production vs. O2 expenditure. The discussion of urea synthesis is essential to understand the needs of ATP in this cyclic maneuver of ammonia excretion, invariable due to amino acid utilization of what ever nature, within the fetal body.
Urea synthesis—the urea cycle starts with L-Arginine that combines with water to cleaves off 2 of it's amino groups as urea, while also forming ornithine that combines with carbonyl phosphate (that is formed by 1 molecule of CO2 and 1 ammonium ion, in the presence of 2 ATP, the latter forming 2 ADP), to form citrulline. One more molecule of ATP is again consumed to be liberated as AMP and PP1 in a reaction wherein citrulline proceeds with also an integral participation of the amino group of L-aspertate to form fumarate, also regenerating L-arginine in the process. Fumarate regenerates L-aspertate to continue the urea cycle in conjunction with the regenerated L-arginine. In this process, an equivalent of 4 high energy phosphates (4 ˜{circle around (P)}) are used for the disposal of each molecule of ammonia.
The Metabolic End Products of Amino Acids Enter the Citric Acid Cycle with ATP Debt; However, they are Vital Fetal Requirements as Discussed Below—
The above mentioned ATP debt is similar to oxygen debt the muscle incurs after intense activity. It is intended to express that in an IUGR fetus the supposedly energy/ATP yielding major food stuff, the ‘protein’ in it's catabolic break down and via it's by-products (through ammonia, during it's non-toxic disposal) expends significant amount of oxygen/ATP with net loss of either or both, before any energy/ATP can be produced later on, in the citric acid cycle. Net loss is the term herein used to denote ATP spent for other than energy-yielding or anabolic purposes or pathways, or oxygen spent in unusually significant amounts. Such net loss incurred even before the entry of the protein metabolic end products into citric acid cycle to generate ATP, as exemplified through the maneuvers of some of the amino acids, is summarized below—
Rest of the amino acids have to invariably expend at least 4 high energy phosphates in a similar manner consequent to their catabolic break down, outside the citric acid cycle (unless the NH4+ is used for synthesis of non-essential amino acids in an IUGR fetus) and no amino acid escapes such fate (except arginine, disposing off two amino groups initially, without expending ATP, as above specified), though some form different intermediate amino acids that have to yet ultimately undergo deamination to form ammonia, and then urea, by using 4 high energy phosphates.
In an optimally growing fetus the ammonium ion (NH4+) and the glutamine (derived from ammonia in tissues) are used for the synthesis of non-essential amino acids, thus maintaining positive nitrogen balance (unlike an adult whose nitrogen intake matches nitrogen excretion) essential for growth. In IUGR, the fetal body protein is used for dire energy needs with net gain of only few ATP. The normal AF urea content is 2.8 mmol/L at 16 weeks and 3.8 mmol/L at 34-36 weeks with increase to term, which is 3 times lower in concentration than it's content in the fetal urine itself. The non-essential amino acids are in turn synthesized from other amino acids/carbohydrate intermediates, and hence can be a suboptimal process in the IUGR fetus that is obviously forced to the verge of negative nitrogen balance. The energy expending urea synthesis may also be impaired in IUGR with consequent oliguria, as urea is a powerful osmotic diuretic, and it is questionable if an IUGR fetus can maintain an optimal blood ammonialevel. Such a need of ATP requiring waste disposal is not encountered in glucose/fatty acid catabolic combustion.
Conventional standardization of food energy for the sake of comparing nutritive values of foods take into account only the kcal of energy they produce per unit mass. The carbohydrates and proteins are considered to produce the same amount of energy, and the fats double that energy. It has to be noted that these comparisons are made in terms of unit mass. Carbohydrates available in nature are packed with substantial water content per unit mass, their H+ and O2 content configured in the same ratio as that of water molecule (as 2:1). On the contrary, the fats are desiccated during their biosynthesis from the parent carbohydrates (review biosynthesis of palmitic acid wherein during steps 5 and 7, a water molecule is lost). Accordingly, one may not be misguided by such comparisons (meant for adults/ex-utero food energy standards) while appraising the fetal energy economics, for the following reasons—
1. The economics of oxygen is highly critical—The value of different classes of fetal fuels has to be determined with great discretion, due to the fact that it has to be measured in terms of calories of energy or ATP generated per unit amount of oxygen expended as the economics of oxygen is strictly accountable due to the relative hypoxia that the fetus has to survive in-utero. Ex-utero, the expenditure of oxygen is not critical, with the unrestricted supply of oxygen inherent to such milieu, except in disease states where there is supply-demand mismatch of oxygen.
2. The STANDARD food energy comparison also does not take into account the ATP expended (vs. ATP generated) by any food group—In other words, the net ATP available for energy expenditure after the metabolic consequences of any food resource is disregarded.
Accordingly, the adult standards of food energy comparisons are irrelevant to apply to fetal nutrition and growth, and proteins that are otherwise considered as equivalent to carbohydrates, and fats considered as superior yielding double in terms of the energy/nutritive value, indeed drastically fall short of such exalted expectations while the fetal energy requirements in the uterine habitat are critically appraised, as is befitting to such eco-system.
The IUGR Diet with Vitamins and Other Essential Nutrients—
It can be stated that the passage of all the essential nutrients through the placenta are impaired in placental insufficiency. Thiamine and the other B-complex factors would not be an exception, and they are better supplied through maternal supplements rather than transamniotic. Such deficits can be primarily due to placental impedance, and secondarily due to hypoglycemia and impaired D-glucose derived-ATP mediated active transport, necessary for their passage into the fetal compartment, as will be extensively discussed in later sections. Thiamine is essential for carbohydrate metabolism in it's catabolic role of the conversion of pyruvate to acetyl-CoA, by pyruvate dehydrogenase complex, as was adequately discussed. If the fetus is deficient in it, substantially increasing glucose loads can be over-whelming to the fetus, and can cause accumulation of pyruvate that can cause pyruvic acidosis and lactic acidosis, and all the path ways where glucose and pyruvate are needed come to a halt. Additionally, pyruvic acidosis in the mother due to pre-existing thiamine deficiency exaggerated after glucose load, with it's beri-beri like symptoms can cause acute/chronic maternal heart failure. Accordingly, planned supplementation of thiamine (initially as 100 mg IM/IV before any glucose supplements, and oral tablets subsequently) is essential to all patients, as malnutritional state for whatever reason (vomiting, alcoholism, food pica, or a suboptimal nutrition/use of prenatal care in developing countries) can be common, and is under-diagnosed in this subset of population. 100 mg of thiamine supplements would increase the levels of thiamine presented at the intervillous space thus ensuring adequate amounts reaching fetal circulation (by achieved Vmax of the substrate transfer mediated by the cell membrane transporters/carriers, as discussed earlier, and this is applicable to all the supplements). Only small amounts of thiamine are stored in the body (25-30 mg), and it's daily need increases as the carbohydrate intake increases. In the adults, unlike other vitamins, daily/short term thiamine requirements are calculated based on concomitant carbohydrate intake. The hypothesis of relative thiamine deficiency in the fetus in the face of impeding glucose load may not be practically found in all growth restricted fetuses, but as there is no easy way of knowing, additional supplements at least would not harm.
Niacin or nicotinic acid, from which NAD and NADP are synthesized, and riboflavin from which FAD is produced in the body, are also essential for optimal carbohydrate metabolism. So also, the folic acid and the phosphate supplements (see the role of phosphate in the section of ‘oxidative phosphorylation’) are essential. It was discussed under the section of protein metabolism, how the fetus has to expend significant number of ATP during the catabolic break down of one molecule of tryptophan, if 1 NAD/NADP were to be synthesized from this amino acid in the fetal body, and many such have to be synthesized, as the requirement of this coenzyme is a mandate to every cell, metabolizing or replicating.
For patients with fetal IUGR on IV D-glucose supplements, with or without also of transamniotic supplements, it is therapeutic to advise a diet mostly of carbohydrates, both simple and complex, for the immediate and for the sustained release of hexose sugars, and the proteins and fats as per pregnancy requirements, but rich in essential amino acids, essential fatty acids, vitamins, and of minerals—called the IUGR diet. The idea is based on the advantage of mostly carbohydrate utilization by the fetus, and likely fat anabolism in the fetal body (a process very essential for developing brain), and of no fat or protein catabolism for energy requirements through excesses of extrinsic supplies (FFA and the amino acids coming across the placenta are best laid down to make up the body bulk of the fetus). The above, by no means imply that the so called non-essential amino acids or non-essential fatty acids are not essential to the fetal growth and maturity. Maternal supply of these are equally important, as per the normal pregnancy requirements, as even the normal fetus may not adequately biosynthesize them. Snacks similar to IUGR diet are advisable between meals and during mid-night. Due to pregnancy pica, and the specific dietary requirements, it is imperative that these patients have a consult with a dietician, and also with a diabetic endocrinologist until they are stabilized.
Along with the diet that usually contains complex carbohydrates, to also ensure intake of simple, rapidly absorbable hexose sugars (as specified in the above IUGR diet), 25 grams of D-glucose powder in water, taken by mouth few minutes before each meal and breakfast, and along with each snack, should be a mandate, incorporated into the maternal dietary protocol for the treatment of fetal IUGR both at home, and in the hospital. At least 1 egg with each meal including breakfast is strongly advised, as this simple and the least expensive diet is a reference protein against which all proteins are measured for their quality and for the completeness of essential and of highly useful amino acids. Based on moderate prevalence of vegetarians by ethnicity/religion or habit, it can be easily accepted by any patient-type. Marine Fish can also be included in the diet. Fish oils were proved to increase birth weight in a study of natural birth weight in Faroe islands (compared to that in Denmark, popular for it's beef industry) where fish is the staple diet (Olsen et al, 1986). The principal marine fish oil is ω3 eicosa-pentanoic acid that competes with the arachidonic acid as a substrate for the cyclooxygenase enzyme, to produce prostacycline rather than thromboxane A2 (T×A2) (Leaf A et al, 1988). Prostacyclin is the nature's potent vasodilator, with probable action at the placental level.
The Accompanying Problems Of Placental Insufficiency—their Causes, Normal Fetal/Pregnancy Adaptation, and Possible Relief by Induced Fetal/Placental Normoglycemia by Transvenous or Transamniotic D-Glucose Supplements Along with the IUGR Diet
It is a legitimate concern that the isolated treatment of impaired placental glucose transfer by therapeutically induced transient episodic hyperglycemic state in the mother can not correct the other problems of feto-maternal exchange, inherent to the placental insufficiency, and all these problems not modifiable and operating together would be still detrimental to the fetal well-being. It is also a critical concern that adequate glucose availability in hypoxic conditions can lead to anaerobiosis and lactic acidosis. The seemingly legitimate concerns as the foregoing, in the face of therapeutically induced normoglycemic status of the fetus, need in depth biochemical exploration. It is the ultimate aim of this writing to detail the intricacies and prove, also by valid scientific data, that the maternal hypertonic D-glucose supplements can indeed correct the other problems of placental insufficiency also to a moderate extent, so that a healthy fetus with acceptable in-utero weight gain can be anticipated. There are few not well known yet superb benefits of restoring the optimal glycemic status at the fetoplacental level that are also enumerated under this section, along with the discussion of the much feared and notorious metabolic problems of placental insufficiency that were well documented in the medical literature, but so far not clinically or theoretically (a critically and a rationally woven thought can be the forerunner of an equally rational clinical solution) alleviated to the satisfaction of a critical or an inquiring reader. They are listed, and later discussed in that order, in the following sections.
1. Improved fetal hypoxia (a demand/supply mismatch of oxygen at tissue level, having immediate or delayed adverse consequences).
2. Improved fetal hypercapnea (above normal blood CO2 that can have adverse effects).
3. Improved fetal oliguria (suboptimal urine production)/oligohydromnios (suboptimal amniotic fluid volume, corresponding to the gestational age)—with or without low fetal urea production.
4. Improved fetal acidosis (excess hydrogen ion concentration in the blood lowering blood pH), including ketoacidosis.
5. Improved fetal hyperlacticemia (excess of blood lactate, with impeding lactic acidosis, mainly due to anaerobic glycolysis) and lactic acidosis, or else pyruvic acidosis that need a special and separate mention apart from acidosis specified under 4 above, as unlike fetal acidosis in general, the improvement of fetal lactic acidosis is consequent to improved fetal hypoxia, or consequent to improved fetal thiamine (and other B-complex factors) levels.
6. Improved fetal hypertriglyceridemia.
7. Improved fetal acquisition of major nutrients like amino acids and fats, and also of minerals, vitamins, and trace elements.
8. Effect of D-glucose on: (a) improved placental L-arginine uptake—for the synthesis of nitric oxide, and for the restoration of fetoplacental vasculogenesis and vasorelaxation; (b) improved placental D-lysine uptake—for it's possible role in placental vasculogenesis—both in turn improving hypoxia and the maternal-placental exchange.
9. D-glucose mediated growth and maturation of vital organs like fetal brain.
10. Improved ATP production (via operating citric acid cycle, secondary to restored fetal normoglycemic status), the ultimate key as the ubiquitous need for all life forms, and for all life sustaining subcellular activities.
The enlisted and discussed accompanying problems of placental insufficiency are either naturally improved by normal fetal/pregnancy adaptations, or else positively altered by the therapeutically induced maternal hyperglycemia or by the transamniotic isotonic D-glucose supplements, and the consequent fetal normoglycemia.
Impaired oxygen diffusion across placenta is a deleterious consequence of placental insufficiency. In the fetus there are many adaptive devices inherently developed, or else manifested in an exaggerated manner due to placental insufficiency, as is described below. If that fails, the therapeutically induced fetal normoglycemic status can surprisingly alleviate such problem.
In the maternal blood, uptake of CO2 and fixed acids (like lactic acid) decreases the oxygen affinity for hemoglobin with further release of oxygen (the double Bohr effect), whereas in the fetal blood, binding of O2 with hemoglobin releases more of CO2 from the blood by the Haldane effect, thus increasing oxygen carrying capacity of fetal hemoglobin. The Haldane effect says that the binding of O2 with hemoglobin releases more of CO2 from the blood. The Haldane effect is also heightened by glucose/ATP mediated arginine active transport, nitric oxide synthesis, placental sinusoidal dilatation, and improved placenta oxygenation, leading to increased oxygen uptake by fetal RBC (in this writing, glucose and ATP are at times referred as if analogous—it is for the reason that glucose is critically acclaimed for it's highest ATP yield, and additionally, it is the therapeutic modality of this invention, further augmenting it's yield).
It is tempting to think that the growing uterus rising from the pelvis may play a significant role in increasing the maternal peripheral vascular resistance, and the falling of cardiac out-put around 28-30 weeks of pregnancy. The aorta bifurcates at the level of fourth lumbar vertebra (L4), and the inferior vena cava commences at the level of fifth lumbar vertebra (L5). The growing uterus can start to exert pressure on these vessels at about 28-30 weeks. Before that period, there has not been any pressure effects on the pelvic common iliac vessels that travel in close association with the lateral pelvic wall, untouched by the gravid uterus, thus causing the lowered peripheral vascular resistance secondary to placental shunt, fully manifest. It is also of note that the increase in peripheral vascular resistance paradoxically correlates with fall in maternal total blood volume, starting at the same time. Considering estrogen effect as uniformly operating through-out pregnancy, it could be only the onset of the mechanical effects of progressively enlarging uterus on the great vessels that could raise the peripheral vascular resistance from 30 weeks onwards, though maintained lower than non-pregnant levels. The forward curvature of the spine is maximum at the lumbo-sacral junction (the convexity of the sacral promontory) that can be exaggerated by maternal lordosis, generally assumed during this stage of pregnancy, both causing pressure effects (as the uterus can not rest wholly onto the abdominal wall in erect posture, as the anterior pelvic inlet can restrict such total postural dependency on the anterior soft structures, and in lying down position, the pressure effects on the great vessels are inevitable).
The placental pooling by the combined effects of increased maternal stroke volume, and due to the decreased peripheral vascular resistance is also important for the reason that fetal heart rate is twice that of the maternal heart rate, and the placental sinusoidal oxygen and substrate reserves presented through one maternal cardiac cycle must adequately serve for sufficient oxygen/substrate exchange through two of fetal cardiac cycles, as befitting of the fetal hemoglobin avidly binding sinusoidal oxygen reserves. The predominantly glucose derived-ATP active transport of L-arginine aids in nitric oxide synthesis that causes sinusoidal/umbilical vessel relaxation with pooling of oxygen-rich maternal blood around the terminal villi with restored flow velocity.
The above discussion of increased affinity of oxygen to fetal hemoglobin that augments oxygen pick up at the placental level, can also give a room for concern of how oxygen can possibly override such affinity to fetal hemoglobin to deliver oxygen at the fetal tissue-capillary level. The issue is extensively discussed in the continuation-in-part (CIP) application that follows.
Impaired excretion of CO2, that is, the exchange of CO2 at the placental site is a reasonable concern in placental insufficiency. The fetus normally has following adaptations for CO2 disposal, that can be improved due to therapeutic maternal D-glucose supplements:
generate 6 molecules of CO2 via glycolysis-citric acid cycle. 3 molecules of CO2 are also produced through 3 molecules of D-glucose inter-conversion into pentose sugars via HMPS that needs the enzymatic action of NADP+, only supplied by ongoing lipogenesis (that regenerates the required coenzyme NADP+) for which optimal D-glucose is also essential. Very little of CO2 is produced in lipid and amino acid catabolic path ways prior to the entry of their intermediates into citric acid cycle. Only few amino acids like glycine, valine, tyrosine, phenylalanine, and tryptophan produce a net 1 molecule of CO2 each in their catabolic break-down. However, fatty acid synthesis generates significant amount of CO2, for example, synthesis of 1 molecule of tryptophan produce a net 1 molecule of CO2 each in their catabolic break-down.
It is obvious that in IUGR, the CO2 production is directly proportional to the food substrates (mainly D-glucose) being available, and being utilized by the fetus (also with concomitant use of molecular oxygen generally, as citric acid cycle, the major generator of CO2 is aerobic), and the placental insufficiency imposes CO2 burden that is only proportional to that of associated hypoglycemia and of hypoxia, and no more (except during oligohydromnios), this stated without giving due regard for 20 times more efficient disposal of CO2 via placental route.
Additional source of fetal carbon dioxide content—The fetus also has additional CO2 source—the amniotic fluid. Amniotic fluid has significantly high CO2 content. Because of it's high diffusion coefficient through any tissue types, CO2 diffuses easily into the amniotic fluid from the highly vascular and metabolically active myometrium (with exponentially increased cellular mitochondria, and very active citric acid cycle that generates significant amounts of CO2) around the whole of amnion, all through pregnancy. The fetus swallowing amniotic fluid also swallows significant amounts of CO2. It is obvious that through the portal circulation CO2 enters the fetal liver, where it is utilized for urea synthesis to dispose of ammonia from fetal blood. Fetal blood so depleted of excess CO2 and also of toxic ammonia, enters the inferior vena cava and then the right atrium, where from the blood is preferentially diverted to the left atrium to enter the proximal aorta, the supplier of more oxygenated and detoxified blood to the fetal vital organs (the heart and the brain).
The above discussion makes it clear that CO2 plays vital role in the fetal body, and the prevalence of hypercapnia is not to be unduly feared for the reason that the CO2 production in the fetal body is actually proportional to both oxygen and carbohydrate utilization, and more importantly the CO2 diffusion across the placenta is deemed to be efficient. It can be further stressed that glucose/oxygen deprived IUGR fetus will have proportionally decreased CO2 production.
However, there are clinical situations in which the so far discussed biochemical norm can be off-set. The very high diffusion coefficient of CO2 that serves the fetus well at the placental site, can also be it's undoing, that in the case of oligohydromnios the amniotic cavity can be highly saturated with CO2, which the fetus swallows falling into a vicious cycle of hypercarbia (hypercapnia) and acidosis. The CO2 can also diffuse into the fetal blood through the umbilical cord. The sequential elaboration of such fetal acidosis is done in the following section-3.
3. The Improvement of Fetal Oliguria/Oligohydromnios/Fetal Acidemia (with or without Low Urea Production)—
There are instances in literature where placental insufficiency was mentioned to be associated with exponential hypercapnia and acidemia (Nicolaides et al 1989). This seems untenable as CO2 production is deemed to be low in IUGR (for the reasons explained above), as the fetus is also deprived of oxygen/D-glucose, the sources of CO2 via the citric acid cycle. There must be an independent mechanism responsible, because the source of CO2 production/hypercapnia is evidently not the D-GLUCOSE in an IUGR fetus, but paradoxically, it is the lack of ongoing D-glucose metabolism materialized as the citric acid cycle, the virtual source of ATP (it can be noted that 4 ˜{circle around (P)} are needed for the synthesis of 1 molecule of urea, as shown in the below simplified equation). In this setting, the possible causes of such findings can be complex, and can be explained as below—
The AF normally is high in CO2, which an IUGR fetus continues to swallow, but there can be impaired disposal of CO2 in the fetal liver. Ammonia normally combines with CO2 in the fetal liver cells to form urea, both being so removed from portal circulation. Synthesis of 1 molecule of urea expends 4 high energy phosphates which means significant energy is expended in making this product of excretion (see also the discussion of urea synthesis in the earlier section of ‘Protein metabolism’). Deficiency of ATP from citric acid cycle due to hypoglycemia or hypoxia, can be responsible for less or no urea formation, leading to fetal oliguria, as urea is a powerful osmotic diuretic. A simplified reaction of urea synthesis is schematically shown below, wherein the 3 ATP resulting in 2 ADP and 1 AMP, instead of 3 ADP, will amount to expending 4 ˜{circle around (P)}—
1. Low or no urea production in the fetal liver and the fetal oliguria can lead to oligohydromnios. However, due to high diffusion coefficient of CO2 (a property that makes it naturally attracted to water molecule), the diffusion of CO2 from the myometrium (that is metabolically very active through pregnancy, generating CO2 via citric acid cycle) into the amniotic cavity will continue, and it's proportion starts to mount steeply due to lowered amniotic fluid volume. Lowered renal perfusion in IUGR (due to fetal auto-regulation of circulation) can also primarily and independently contribute to oligohydromnios, and the amniotic cavity can be virtually a small sac of carbonated water for the fetus to swallow.
2. With exceeding CO2 content in the AF, even for small amount of it swallowed, the fetus will be swallowing fluid highly saturated with CO2 that will be entering into the fetal blood via portal circulation, but not disposed of as urea due to impaired urea cycle, and will be invariably reflected in the umbilical artery via it's transit to the placenta, where it may be disposed off. CO2 can also diffuse into the umbilical cord from the AF. In the absence of urea production and progressing oligohydromnios, a vicious cycle of CO2 accumulation sets up within the fetal blood.
3. Though the AF is known to contain the amino acids (for the needed L-aspergine, and L-arginine for urea synthesis) in a proportion similar to maternal plasma, still sufficient amounts of D-glucose, and ongoing citric acid cycle are required for the significant amount of ATP needed for urea production. It was earlier noted that both the specified amino acids are also regenerated in the cyclic maneuver of urea synthesis, implying ATP availability as critical and paramount.
It can be summarized that fetal oliguria can be primarily due to renal hypoperfusion, or primarily due to suboptimal urea production, or a combination of both in severe cases. It is obvious that improved fetal D-glucose levels and adequate ATP synthesis deemed to operate in optimal urea production leading to osmotic diuresis, can break the vicious cycle of fetal oliguria/oligohydromnios.
The causes of acidosis in IUGR—Acidosis is an anticipated concern in acutely or chronically distressed fetuses. It can be more so in the setting of fetal IUGR—due to the combined effects of (1) lactic acidosis secondary to hypoxia, (2) keto-acidosis secondary to hypoglycemia, and (3) depleted reserves of the bicarbonate base (HCO3−) that is generally replenished through the citric acid cycle. The depletion of HCO3− base in a similar setting can be clinically seen in diabetic keto-acidosis, wherein despite the prevailing low levels of blood HCO3−, by mere insulin supplements and by the restoration of blood glucose utilization via the citric acid cycle, blood HCO3− is replenished, and the acidosis corrected. In this clinical setting of diabetic ketoacidosis, supplemental HCO3− is rarely needed, except in extreme life threatening conditions of acidosis.
In IUGR, restored normoglycemia, and fetal fatty acid synthesis as a result, not only regenerates oxidized coenzymes NADP+ but also uses hydrogen ions. 28 hydrogen ions generated through HMPS are used in the synthesis of one molecule of palmitate from acetyl-CoA, and melonyl-CoA. During the later months of pregnancy, the lipogenesis that takes place in a normoglycemic fetus can dispose off enormous amount of hydrogen ions from the fetal body, generated mainly via universally ongoing HMPS. During hypoglycemia there will not be any lipogenesis. On the other hand, lipolysis and beta oxidation are initiated for energy requirements, further made more prominent by decreased insulin levels secondary to hypoglycemia (insulin is anti-lipolytic that normally antagonizes the many lipolytic hormones in the body—like the growth hormone, the adrenocorticotropic hormone, and the glucagon). But in the absence of sufficient amounts of D-glucose and lack of oxaloacetate, acetyl-CoA produced via beta oxidation of lipid break-down finds no entry into citric acid cycle, and is fated to produce ketone bodies which are moderately strong acids. Once they are formed, even if glucose is made available, the ketone bodies are oxidized in preference to glucose, thus saturating the oxidative machinery. Normoglycemia can compensate for relative hypoxia by 33%+400%+10%, by various metabolic consequences, but obviously oxygen can not compensate for hypoglycemia, and the related metabolic consequences.
Acidosis can also be produced when IUGR is also associated with fetal oliguria/oligohydromnios, a grave clinical concern that can virtually lead to a moribund fetus. This scenario was described elaborately in the immediate preceding section-3.
This is discussed separately from fetal acidosis in general, as fetal lactic acidosis is unique in that, unlike other types of metabolic acidosis, it is only cleared by resolution of hypoxia, it's causative pathology. The D-glucose supplements can correct the inciting pathology by improving fetal hypoxia by various means, as discussed in the section of ‘Improvement of fetal hypoxia’. If not, supplemental oxygen therapy can alleviate acidosis as will be seen in the elaborate discussion in a subsequent section. Thiamine deficiency can also cause lactic acidosis/pyruvic acidosis, and can be relieved by thiamine supplements, advocated as a mandate to the D-glucose supplements.
During hypoxia secondary to placental insufficiency, the fetus can resort to anaerobic glycolysis that generates significant amounts of lactate, but production of only 2 ATP from 1 molecule of D-glucose. Due to lack of pyruvate, the usual end product of glycolysis under aerobic conditions, the citric acid cycle is not made possible. Only the restoration of normoxia (optimal blood/tissue oxygenation that meets the demands) can relieve lactic acidosis, when pyruvate is regenerated from lactate via reversal of the step catalyzed by lactate dehydrogenase, and/or by thiamine supplement, if needed, when pyruvate is oxidized to acetyl-CoA by pyruvate dehydrogenase to enter citric acid cycle, greatly enhancing the reversal of the reaction generating pyruvate from lactate (see also the last SECTION of this specification ‘Neonatal care of an IUGR baby’).
Lactate is an important fetal substrate being constantly supplied to the fetus by the placenta. As glycogen formation is not without significant amount of ATP consumption, the placenta stores glucose less as glycogen, and more as lactate, the predominant placental carbohydrate reserve that it supplies to the fetus throughout gestation, the best example of nature's efficiency and wisdom of what looks like nature's folly. The glycogen synthesis expends 2 ATP for each glucose molecule to be incorporated, whereas lactate production generates anaerobically 2 ATP with a total potential gain of 4 ATP in it's making, compared to the alternate means of placenta storing glucose as glycogen. The fetal brain, heart, and skeletal muscle can convert lactate into pyruvate, via the lactate dehydrogenase reaction, when NAD+ is converted to NADH+H+ to generate 3 ATP aerobically, while the ATP yield to the fetoplacental unit is similar to that of aerobic glycolysis. The lactic acidemia becomes a metabolic concern only after prolonged anaerobic glycolysis of glucose by the fetus during unrelenting hypoxic conditions as in placental insufficiency, whereas normally lactate is the fetal fuel just like D-glucose, only efficiently saved. Nonetheless, it can not be concluded without saying that ‘no two metabolic products cause more apprehension to the explorers of fetal medicine than the lactate/lactic acid and the CO2, as it is hard to fathom when they may turn against, as similar to man's tools, the swords and the guns, they also both save and kill!
Persistent fetal lactic acidosis can be reflected in the AF (amniotic fluid), as kidney is an effective organ both in metabolizing and excreting the lactic acid, and the fetal urine passed into AF can reflect the fetal lactic acid levels. Fetal kidney also excretes progressively increasing amounts of creatinine as the organ matures in it's function. Thus AF creatinine content is a reflection of fetal maturity.
The placenta metabolizes significant amounts of glucose anaerobically, and the lactate can diffuse into the AF, the maternal circulation, or into fetal circulation, but mostly it will be supplied to the fetus. The maternal venous blood lactic acid/pyruvic acid ratio is 10, whereas it is 12 in the fetus. When the maternal food consumption itself is low, as during the stretch of time between dinner and breakfast, the placenta supplies it's reserves of lactate to meet the fetal needs. The placenta metabolizes 80% of glucose extracted from maternal blood anaerobically, to convert it into/store it as lactate (L. Myatt). In fact, the placental uptake of glucose is more (50-60%) than the fetus during early months of pregnancy, and it declines only towards term when the placental pentose phosphate pathway (the HMP shunt, predominantly required for placental elaboration) and other previously dominant anabolic pathways gradually diminish (L. Myatt). Lactate utilization accounts for 25% of oxygen consumption in a normal fetus, and contrary to expectations, high fetal lactate levels will not account for/result in fetal acidosis (J. A. Low). High rate of placental permeability to lactate was observed in hemochorial placentae, as the human placenta. During IUGR with associated hypoxia, the fetus becomes the sole producer of lactate/lactic acid, and the placenta becomes an important site to clear the excess fetal lactic acid, and ceases to be the lactate producer/supplier, as there appears to be an impaired H+/lactate co-transport in the basal membrane of the syncytiotrophoblast in term or pre-term IUGR pregnancies, compared to the appropriately grown controls (P. Settle et al). It seems reasonable to contemplate that the intrinsic glucose needs of the placenta itself having not been met in the setting of IUGR, the placenta loses it's reserves of stored lactate, so that it can not supply the usual provisions of lactate to the fetus.
Econamides and associates (1990) who measured fetal triglyceride (TGD) levels demonstrated fetal hypertriglyceridemia that correlated with the degree of fetal hypoxemia. Barker and colleagues (1993) at the United Kingdom's medical research unit had over 20 years researched the causes of adult mortality and morbidity in relation to possible adverse intrauterine life, and found increased risks of hypertension and atherosclerosis in the context of IUGR.
In this writing, the author attributes the adult hypertension and atherosclerosis of above studies to the mode of hypertriglyceridemia produced in the IUGR fetuses (as discussed below) that could be persistent for significant part of intrauterine life. Experimental results in animal and in human atherosclerosis studies suggest that the fatty streak represents intimal lesions resulting from focal accumulation of lipoprotein in the vascular intima. Recruitment of leucocytes to the nascent fatty streak and their adhesion to vascular intima are further made easier due to sluggish laminar flow because of polycythemia and of hyperviscosity of blood in the IUGR fetus. In this set up at least some amount of thrombotic reaction in the focal atheromatous area is possible. As per the ‘Virchow's Triad’, the thrombosis of a vessel wall depends on three factors—the velocity of the blood flow, the viscosity of the blood, and the nature (injury, if any) of the vessel wall, all being present in the IUGR fetuses in an adverse manner. Accordingly, a ground work is already laid out in-utero, as a thromboatheromatous plaque in the vessel wall, as an operation of Virchow's triad in the set up of persistent hypertriglyceridemia of intra uterine life that can likely progress and manifest as atherosclerosis and hypertension in adult life. Even a small lesion in intrauterine life can be magnified as the baby grows, and in adult life it can assume significant proportion, similar to a mole or a scar on a child's body becoming proportionally bigger in the adult life.
The initiation and the perpetuation of fetal hypertriglyceridemia in fetal IUGR can be as follows—insulin is a potent positive stimulus for lipogenesis, and a negative stimulus for lipolysis. It inhibits the activity of the hormone sensitive lipase (that is different from the lipoprotein lipase) responsible for lipolysis, thereby preventing the release of not only FFA from the fat stores, but also of glycerol. In IUGR, there is prolonged and persistent hypoglycemia causing hypo-insulinaemia (or hypoinsulinism) resulting in the unopposed action of other hormones like the GH (growth hormone), glucagon, and the ACTH (the adrenocorticotropic hormone) that causes lipolysis through their stimulatory effect on the hormone sensitive lipoprotein lipase. How ever, because of the lack of oxygen needed for beta oxidation of the released FFA, they are not used. In this setting, the esterification of FFA with glycerol in other tissues results, causing fetal hypertriglyceridemia or hypertriacylglycerolemia as is usually seen in adult diabetes.
There can be additional factors operating in the young adult life of the SGA infants who suffered IUGR. Despite hypoglycemia and secondary hypoinsulinemia (hypoinsulinism) the IUGR babies who survived adverse intrauterine life have been shown to mount adequate insulin response postnatally. This is evidenced by the fact that diabetes, if at all manifests, is only transient in the SGA infants during their neonatal life. However, diabetes can be a problem for them as young adults, as the growth restricted islet cell mass of pancreas (due to persistent hypoglycemia of intrauterine life) that is hypoplastic (in proportion to the fetal glycemic status) but not vestigial, may be adequate to cope up with the blood glycemic demands of early childhood, but not of the young adulthood, when insulin requirements increase. Moderate hypoinsulinemia again becomes manifest, with the consequent lipolysis (insulin being anti-lipolytic) and hypertriglyceridemia (as described above). For significant number of years it can go unsuspected and undiagnosed, due to it's uncommon age prevalence, and no associated family history. This will further add to and result in ongoing atherosclerosis and hypertension. The set up is similar to untreated adult diabetes mellitus, with it's associated risks of hypertension, atherosclerosis, and of the early onset coronary artery disease. For such clinical manifests, the adult diabetes is categorized as a coronary artery disease (CAD) risk factor, and the imposed risk considered significant enough to be categorized as equivalent to diagnosed/established CAD.
It was adequately described how glucose is transported through cell membrane by facilitated diffusion in the section ‘The biochemical basis for hypertonic D-glucose treatment’. In that context it was also discussed how the Michaelis-Menten equation is an expression of the relation of substrate concentration and the resultant rate of an enzyme/hormone or of a cell membrane/cytosol located substrate carrier mediated chemical reaction—either by active transport or by facilitated diffusion. It was discussed with figurative illustration (
Michaelis-Menten equation can also be applicable to the transport of all the placental substrates (discussed under this section) whose concentration can be greatly improved at the placental interface (by the IUGR diet implemented to all the afflicted mothers) such transport further enhanced indirectly by induced normoglycemic status improving ATP production that heightens the placental concentration of maternal substrates by ‘active-transport’, operative for a great many substances direly needed by the fetus, but present in lower concentrations in the maternal compartment.
The amino acids are needed for anabolic needs like lay-over of fetal body muscle mass, and biosynthesis of specialized products such as (a) hormones, (b) enzymes and coenzymes, and (c) neurotransmitters, to mention a few.
It is a saving provision that the AF contains amino acids in the same proportion as the maternal extracellular fluid, and the fetal swallowing of AF can be a significant means of their acquisition, but not optimal, and hence the contribution of placental transfer is invariable.
Amino acid transport across the microvilli of the trophoblast can be achieved by different means and influences, as follows—
The IUGR fetus, and the effect of IUGR diet—The amino acids may not be adequately acquired by the fetus in the setting of placental insufficiency. There is documented evidence in the literature that the cordocentesis of SGA fetuses afflicted with growth restriction in-utero showed lower amino acid levels, compared to their appropriately grown (AGA) counterparts, and this especially involved essential amino acids that the placenta must transfer. As the levels of placental transporters were found to be unaffected in the placentae of growth restricted fetuses, it can be deduced that it is the effect of the failed placental elaboration, and reduced surface area that influence the amount of amino acids to be transported. The beneficial clinical manipulation through IUGR diet is based on the fact that the rate at which the amino acids transport through a membrane by facilitated diffusion, based also on Michaelis-Menten constant, depends on—
The fetal heart rate being 140 per minute, and as the cycle's systolic time is unchanged at any rate, to make such purposeful high rate and a better systolic villus capillary filling effective, the placental carriers must function in a ‘speed mode’ so as to carry enough of needed fetal substrates. Hence, if v1=Vmax, by a manipulated high substrate (S) concentration, higher will be the substrate transfer. The maternal heart rate being only half that of fetal heart rate, the pools of placental sinusoidal structure normally compensate with enough of such substrate reserve lasting through two of the fetal cardiac cycles.
Restored Transcellular Amino Acid Transport within the Fetal Body Secondary to Normoglycemia and Normalized Insulin Effects—
It is of great significance that glucose supplements and the consequent fetal normoglycemia bestow the double benefit of heightened transcellular transport of both glucose and of the amino acids within the fetal body, via the normalized hormonal effects of insulin on both.
Only few substances are soluble in water and also in the lipid bilayer of the cell membrane, such few of physiological importance being the oxygen, carbon dioxide, and the FFA. And the primary factor that determines how rapidly a substance can diffuse through the lipid matrix of a cell membrane is the rate of the solubility of the substance itself. The fatty acids themselves being lipids, solubility barrier in the lipid bilayer of the cell membrane should be of no concern, and they are easily diffusible by means of ‘simple diffusion’ across the lipid layer of cell membrane requiring no carriers, such diffusion proportional to the concentration gradient.
The major factor in determining the transfer of free fatty acids across the placenta is the maternal levels of circulating free fatty acids. The function of Human Placental Lactogen (HPL) is blocking of the peripheral uptake and utilization of glucose by maternal tissues, while also promoting the mobilization of free fatty acids (FFA) from the fat depots, for utilization by the mother. The elevation of serum total lipids, phospholipids, and of FFA during pregnancy is enormous, with a progressive increase towards term. The total lipids increase by 46%, and the FFA by 60% during 37-40 weeks of pregnancy. Such high values assure high maternal gradient across the placenta for simple diffusion of lipids and the FFA (both the essential and non-essential free fatty acids) into the fetal circulation. The fatty acids so derived contribute to the structural components of the cell membranes, and to the cellular architecture of the brain that is predominantly lipid. The rising albumin levels of the fetus can further help to carry, and mount the levels of fatty acids. The therapeutic maternal hyperglycemia can also spare FFA utilization to some extent by the mother.
The increased content of maternal essential fatty acid levels via IUGR diet will also proportionally increase placental transfer of these fatty acids by the similar principle of simple diffusion. If the FFA levels were found by the investigators to be much lower in the fetus than the mother, it probably is because they are immediately incorporated into the fetal anabolic processes that further provides needed concentration gradient, or else the simple diffusion of the FFA would cease. More over, the enormous rise of FFA in the mother is purposeful. The molecular weight of the concerned FFA has a bearing on the kinetics of diffusion, the low molecular weight FFA like the palmitic acid diffusing more rapidly than the high molecular weight FFA like the oleic acid, though the latter is a predominant FFA of the maternal adipose tissue. The palmitic acid is indeed the integral building block of the rapidly developing fetal brain, as will be seen in the later discussion, and hence also is the one most needed from the maternal compartment.
Many of circulating fetal elements that are absolutely essential for it's optimal growth, like calcium, iron, magnesium, and iodine are found to be at higher levels in the fetal side than that of the maternal side, and they are not synthesized by the fetus.
To cite a clinical example, in the case of iron transport, despite severe anemia clinically manifesting in a mother, her fetus is rarely anemic. That is why it was appropriately said that the fetus thrives at the expense of it's mother. Such optimal fetal growth in adversity is achieved by the transcellular, ATP dependent and of a carrier mediated active transport, accomplished in the placental tissues directed to minerals, vitamins, and the trace elements that can be normally less in quantity in the maternal blood, yet are absolutely needed more by the fetus.
Active transport—The active transport obeys the same laws of chemical combination of the substrate with the carrier molecule, and a specific carrier molecule (for example—calcium binding protein, or the phosphorous binding protein) is required to transport each type of, or each class of substance(s) having natural affinity for it's carrier that makes the two of them combine readily on the outer surface of the cell, yet on the inside of the cell, energy in the form of ATP is needed for their dissociation, this may also needing an enzyme catalysis.
(a) Iron transport—iron is transported through the placental tissue by active transport. Over all, about 375 mg of iron is needed by the fetus to be deposited as hemoglobin in it's red blood cells. During the first few months of pregnancy, the placenta grows rapidly and enormously, yet when the fetal growth can be only described as diminutive in comparison. It is for the reason that placenta avidly accumulates proteins, calcium, and iron, to be stored in and used during the later months of pregnancy when the absorption of some of these elements by the maternal gastrointestinal system is less than optimal. Iron accumulation by the placenta is more rapid than that of calcium and of the phosphates, and in fact it is concentrated in the progestational endometrium during the luteal phase, even prior to implantation. This iron, ingested by the trophoblastic syncytial giant cells of the embryo is required for the formation of red blood cells even at this stage. One third of iron at term is stored in the fetal liver, intended for the use of the neonate during the early months of life. Placenta functions similar to the fetal liver from early on, in terms of the storage of both carbohydrates and iron, to be liberated and furnished when the fetal demands are more. The D-Glucose supplements with restored acquisition of glucose by the placenta and the fetus can enhance the process of active transport of iron by readily available supply of ATP. It can improve the fetal MCHC. It in turn can regress the fetal polycythemia, and reduce the excessive production of the fetal erythropoietin. Though they are mainly the secondary effects of fetal hypoxia, yet improved fetal iron and improved MCHC can have positive bearing in this setting.
About 23 grams of calcium and 14 grams of phosphorous are accumulated by an average fetus. Half of this gain is during the last 4 weeks of pregnancy, when also there is rapid bony ossification, and maximal fetal growth. As a saving measure, urinary excretion of calcium falls during pregnancy, coupled with that of increased intestinal absorption, probably due to estrogen influence. Only extreme maternal deficiency of calcium will reflect in the fetus as congenital rickets, which indicates that the maternal stores were very deficient, or that the pregnancy defenses failed by some other means. In the case of calcium, there are additional factors that are also at play in the mother, like the Vitamin-D/parathyroid hormone level, just as in the non-pregnant state, and the placental cells are no exception to that influence (see also the calcium-magnesium antiport below, with regarding placental calcium acquisition). Just as calcium, phosphorous is also physiologically linked to the above influences. The foregoing discussions of the metabolic path ways of major food stuffs made very clear of the need of phosphorous in all anabolic and catabolic processes through it's vital role as ATP, generated by the participation of inorganic phosphate (H2PO4−, the dihydrogen phosphate ion) in the life sustaining process of the mitochondrial oxidative phosphorylation.
Magnesium is very essential to the fetus because of it's need in all reactions where ATP/ADP are the substrates. It is transported through the cell membrane probably by active transport involving the calcium-magnesium antiport (an antiport system moves two molecules in an opposite direction) in the same manner as the sodium and potassium ions are transported involving the sodium-potassium ATPase (in the sodium-potassium antiport, the active transport involves potassium, an intracellular cation coming into the cell, whereas sodium, an extracellular cation getting out, and the system normally transports 3 of sodium ions to the outside of the cell, and 2 of potassium ions to the inside).
Magnesium is mainly an intracellular cation, and calcium an extracellular cation. In the magnesium-calcium antiport, involving calcium ATPase, magnesium ions are probably transported into the cell, and calcium ions to the outside. This explains the bidirectional transport of calcium in the mammalian placentae. Despite the outward flux during calcium-magnesium antiport, calcium transfer is independently controlled and achieved by the facilitation of vitamin-D and the parathyroid hormone, and also by passive diffusion down an electrochemical gradient via calcium channels, as maternal calcium levels are maintained far higher than the non-pregnant levels. Further more, fetal net acquisition of calcium is aided by calcium binding protein that protects the intracellular calcium from becoming too high, any intracellular excess being not amicable to the normally intended cellular functions.
(c) Iodine transport—the placenta can actively transport iodide ion by means of active transport, as iodide is essential for the synthesis of the thyroid hormone from the fetal thyroid gland, and the maternal thyroid hormone crosses the placental barrier only to a limited extent, as obviously, it will impair the development and maturation of fetal thyroid gland by negative feed-back, and the hormone secreted by the fetus deemed to be imposing such feedback.
Fetal acquisition of minerals and trace elements through amniotic fluid (AF)—while all the inorganic substances like the minerals and trace elements can pass through the placenta only by active transport, they can yet diffuse into the amniotic cavity (in dissolved/suspended state in maternal extracellular water), via the intercellular and intracellular canalicular system all through amnion by means of passive diffusion that needs no energy expenditure. The minerals and trace elements are present in the AF in the amounts proportional to their concentrations in the maternal extracellular fluids. The fetus can swallow these elements of the AF, but obviously not in amounts that can correct the deficiency imposed by normally needed major placental concentration.
(d) Vitamin transport—the vitamins are transported across placenta by ‘active transport’ expending ATP, and are found to be in much greater concentrations on the fetal side. The ascorbic acid (the vitamin-C) levels on the fetal side are found to be thrice that of the mother.
The mechanism of active transport, and it's relevance to therapeutic glucose supplements—In states of ATP depletion as in IUGR, the transfer of the essential minerals and trace elements is invariably diminished, adding to the other major problems of this disease state. Glucose via citric acid cycle being the major generator of ATP, the therapeutic D-glucose supplements relatively improve the diminutive transport of these very essential fetal growth factors, and operating irrespective of maternal gradient and in conjunction with the normally surplus provision of available cell membrane ‘carriers’—it can effectively override placental insufficiency to a moderate extent
With vital control of insulin on the transcellular glucose transport, it is a legitimate question how the babies of mothers with uncontrolled diabetes are growing to be macrosomic. When insulin controls the transporters, how glucose is overcoming the placental barrier imposed by insulin deficiency or resistance in poorly controlled diabetic pregnancy ?
Before the advent of insulin, diabetic women conceiving and carrying the baby to term were rare. This clearly denotes that even the endometrial (decidual) cells need insulin for glucose transport to be stored in the form of glycogen to sustain the growth of the early conceptus. Decades ago, untreated diabetic women also suffered secondary amenorrhea, indicating the influence of insulin and of the required glucose on the proliferation of estrogen-primed endometrium that needs to be shed later. Accordingly, it is obvious that the diabetic pregnancies became common clinical concern after the insulin therapy became the indispensable tool of the obstetricians.
Maternal diabetes with fetal macrosomia is probably mostly evident in type II obesity associated diabetes in whom central obesity is the culprit, the obese adipocytes in this setting being capable of producing peptides including cytokines that are capable of modulating the insulin response by causing first insulin resistance, and then hyperinsulinemia. The hyperinsulinemia can in turn lead to down-regulation of cell receptor sites for insulin, on the insulin-sensitive tissues. Thus the target tissues over time become markedly insulin-resistant in these patients, who in turn need some treatment intervention. Marshall R N et al and Posner B I et al in 1974 demonstrated that the placental binding protein of insulin is similar in molecular weight and function to the insulin receptor protein found on the fat and on the liver cells, that are also unaffected by a subject's insulin resistance. When diabetic women conceive, the placenta just as the fat depots being unaffected by maternal diabetes, the maternal hyperinsulinemia will proportionately increase glucose transfer across the placental interface, leading to fetal islet cell hypertrophy and then fetal macrosomia.
Nitric oxide (NO) is a potent vasodilator throughout the body, and it is synthesized from the essential amino acid L-arginine by the action of Nitric oxide synthase. It uses NADPH+H+ as a cofactor. Nitric oxide has a very short half-life of 3-4 seconds, which means it needs to be continually synthesized. As L-arginine has to be supplied by the mother, increased supplements of essential amino acids via IUGR diet, by improved substrate (S) concentration and also Vmax, will improve it's placental intake/transfer so that it can be effective locally—in the spiral vessels, in the villous capillaries, and also in the umbilical circulation for generating the needed nitric oxide so as to facilitate their vasorelaxation.
The transplacental transport of certain essential and the non-essential amino acids occurs by active transport as specified earlier, for which ATP is essential. Maternal hypertonic glucose supplements improve the ATP synthesis, and thereby the active transport of L-arginine at the placental interface, apart from also providing the needed NADPH+H+ generated from the carbohydrate metabolism, involving pentose phosphate pathway (the placenta itself has active pentose phosphate pathway). As active transport is also the mechanism by which L-arginine is transported into the endothelial cells of any vessel wall, the glucose induced active transport of L-arginine into the umbilical vessel endothelial cells can lead to the synthesis of nitric oxide in the vessel wall that can restore umbilical vessel vasodilatation. Such improved impedance both in the placenta and in the fetal vessels shall have great bearing in incrementing both the flow velocity and of the flow volume in these vessels to over-ride the ‘critical closing pressure’ consequently relieving hypoxia, and also of the accompanying multitude of adverse effects involving the placental exchange.
The following researchers from Chile, South America, recently made interesting observations of the role of Nitric Oxide in the growth of the fetoplacental unit and it's circulation, and also of the effect of D-glucose in L-arginine transport through cell membrane—
Krause et al (2011) in their placental study proved that nitric oxide is essential in placental trophoblastic invasion, cellular respiration, and also in maintaining the vascular tone. They further proved that it also represents the main vasodilator function of the placental vessels, and that it participates in placental vasculogenesis through the angiopoietin signaling molecules. Hence it's role is important even in alleviating prevailing placental pathology.
Sobrevia et al (2009) observed that D-glucose and insulin increased L-Arginine transport and cGMP accumulation in the Human Umbilical Vessel Endothelial cells (HUVEC). It is plausible as noted by the observations of these researchers that glucose enhanced (and insulin mediated) active transport is involved in the specified L-arginine transport.
Casanello et al (2009) in the research involving HUVEC of normal and IUGR pregnancies, observed that the HUVEC of IUGR exposed to both normoxia (optimal amount of tissue oxygen that meets metabolic demands) and hypoxia, and HUVEC of normal pregnancy exposed to hypoxia, exhibited reduced L-arginine transport, and reduced nitric oxide synthesis. They concluded that the IUGR cells were either not responsive, or maximally affected by hypoxia.
But the above observations by Casanello et al can be the result of lack of both glucose (needed for synthesis of ATP for active arginine transport) and of oxygen in the IUGR affected vascular endothelial cells (HUVEC), whereas it was due to lack of only oxygen (hypoxia) in unaffected normal umbilical vessel endothelial cells (HUVEC) that can otherwise transport L-arginine (during normoxia) via active transport mediated by glucos that they are not deficient in.
Other positive effects of fetoplacental nitric oxide production—Wilcox et al in 1989 reported reduced platelet (PLT) count in the cord blood collected at delivery from both normotensive and hypertensive patients, whose fetal Doppler umbilical cord studies exhibited high placental vascular resistance. They hypothesized that there is increased PLT aggregation and consumption, as a result of the said placental pathology of increased vascular resistance. Or, the primary pathology could be a local imbalance in favor of excess thromboxane A2 (responsible for potent vasoconstriction and PLT aggregation) and consequent damage to placental micro-structure, resulting in placental insufficiency (Nicolaides K. H and Campbell S, 1991). Nitric oxide apart from causing vasorelaxation, also acts on platelets to effectuate PLT anti-aggregation (Kniss D A. 2001). Essentially, in the above study of Wilcox et al there could be impaired Nitric oxide production, resulting both vasoconstriction and also PLT aggregation/consumption.
It can be concluded that hypertonic glucose supplements not only directly relieve hypoglycemia, but also by effectuating ATP-arginine induced nitric oxide synthesis, indirectly induce vasculogenesis/vasorelaxation, and further alleviate the placental vascular damage/impaired exchange of uteroplacental insufficiency, and so breaks the vicious cycle.
Debatosh Datta (2007) observed that monomeric lysine was found to expand biomass (cell population) at the least possible time compared to other physicochemical means. It was also observed that D-lysine can induce neovascular growth in all tissues types.
In the placental bed, D-lysine still has to be transported into the cell through active transport expending ATP, to exert such vasculogenesis. In case of established trophoblastic failure, D-glucose supplement is crucial to break the vicious cycle of placental insufficiency (as was described above in case of L-arginine deficiency), and to stimulate trophoblastic villous elaboration, by supplying ATP needed for placental D-lysine uptake.
No organ in the developing fetus needs more glucose than the fetal brain. Whereas all the tissues need glucose for energy, and as the currency of ATP (that is, for catabolic purposes), the fetal brain needs it as it's very building blocks (for anabolic purposes). So it can be said that in the fetal organogenesis, in the brain's rapidly progressive architecture, glucose is the brick, whereas everything else, including oxygen (ignoring it's gaseous form) serves only as it's cement. Moreover, glucose also has to additionally supply needed energy in the brain, as elsewhere. In this context, the requirement of glucose in the developing fetal brain as being enormous, is but anticipated. Unless one explores the biochemical architecture of the brain, it is hard to fathom that all it's lipid components indeed took their origin from glucose, and it's quantity incorporated also can be unimaginable to a casual reader. It is for the reason that the brain's integral lipids are very long chain fatty acids, the most important being the cerebronic acid, made up of 24 carbon atoms, that require ⅓rd more of acetyl-CoA molecules than the 16 carbon palmitic acid, the most synthesized fatty acid of the fetal body. Hence the most fundamental, and some so far unexplored issues of fetal brain's biochemical architecture, and the best of glucose/oxygen economics warrant discussion here, especially in the context of even normally prevailing relative hypoxia in-utero. The inquiry that by what biochemical path ways the excess (in absolute numbers) of glucose/oxygen expenditure by the fetus is normally curtailed in this setting is crucial, as it was never explored before with the needed emphasis on the critical glucose/oxygen economy.
Symmetrical vs. asymmetrical fetal growth restriction—As defined in the introductory paragraphs, fetuses or neonates whose estimated/attained birth weights are less than the tenth percentile are considered growth restricted, as per the prevailing US guidelines, this being more stringent than the fifth percentile that is the standard cut off in other countries.
The IUGR fetuses or SGA babies are classified either as being symmetrically small, or asymmetrically small. This discretion is clinically significant that symmetrically grown IUGR fetuses or SGA infants shall not be mistaken as premature.
At the onset of the third trimester the fetal head is normally larger in comparison to it's length and the abdominal girth, though the fetus's earlier striking tadpole configuration is less obvious at this time. Such disposition begins to change even more, starting 29th week of gestation when as a result of the initiation of fetal lipogenesis and of the glycogen storage in the liver, the abdominal girth/growth accelerates. The head and the abdominal circumferences equalize by 34 weeks, which however is not the case in the asymmetrically grown IUGR fetuses (Reiss R E).
The above discussion highlights that even in IUGR, the nature's defenses strive hard to preserve the integrity of fetal vital organs, especially the brain. However, a failed potential for intellectual fulfillment is not rare in this subset of pediatric population, as measured by low IQ, or as suboptimal educational attainment. In human, the myelination of brain is most rapid from the 7th month of fetal life, the time when the fetal brain is most susceptible to the effects of under nutrition, for whatever reason. This is also the time the fetal IUGR usually makes itself manifest clinically. This makes the objective of diagnosing the fetal IUGR an imperative from early on, and the treatment of every pregnancy so afflicted a much sought after clinical endeavor so that no child will be losing the innate potential it is genetically endowed with.
Fetal Lipogenesis, and it's Role in Fetal Brain Development—
The human brain is predominantly made of fats, comprised of mainly phospholipids and of glycolipids as the major structural components. The outlines of these biochemical entities were already specified in the section of ‘Lipid Metabolism’, and they are herein elaborated.
The phospholipids of the brain are sphingomyelins, composed of—
That is, the brain's phospholipids made of sphingomyelin, essentially consist of: palmitic acid, serine, cerebronic acid, and phosphoryl-choline (choline & phosphoric acid).
The glycolipids of the brain are cerebrosides. They also contain sphingosine-fatty acid combination (the ceramide) as in sphingomyelins, but a galactose moiety is attached to the ceramide instead of the phosphoryl-choline residue found in the sphingomyelins, and it's structural elements are as shown below—
That is, the brain's glycolipids made of cerebrosides essentially consist of: palmitic acid, serine, cerebronic acid, and galactose.
By what was earlier discussed, it was made clear that 8 acetyl-CoA units or 4 glucose molecules are required in the biosynthesis of 1 molecule of 16-carbon palmitic acid. Similarly, the biosynthesis of the 24-carbon cerebronic acid needs 12 acetyl-CoA, or 6 glucose molecules as structural elements, which however is achieved by chain elongation.
Microsomes are the site of chain elongation for fatty acids with even number of carbon atoms, starting from C10 upward, using melonyl-CoA as the 2 carbon donor, and NADPH+H+ as the reductant, in a manner similar to fatty acid synthesis, as described earlier with reference to the biosynthesis of palmitic acid.
The synthesis of very long chain fatty acids in the fetal brain needs significant expenditure of both glucose and oxygen. However, in this anabolic process of fetal brain, staring from glucose molecules as the originators, the brain's fatty acid synthesis also generates moderate amount of ATP. It is for the reason that at the outset it involves the ATP generating catabolic steps of glucose in the pathway of glycolysis, yielding the acetyl-CoA that are needed as the building blocks of palmityl-CoA. It also needs to be duly noted at this point that the brain's glycolipids and phospholipids contain both cerebronic acid (of 24 carbon units) and palmitic acid (of 16 carbon units), which together amount to a need of a total of 20 acetyl-CoA (and of 10 glucose molecules) altogether, for the formation of 1 molecule of either a glycolipid or of a phospholipid. But in the following discussion the focus is confined to the synthetic requirements of cerebronic acid, the longest chain fatty acid, because for the needed calculations the exemplified cerebronic acid can serve the purpose.
The initiating steps of the lipogenesis via Glycolysis-Abbreviated Citric acid Cycle (the LGACC) in the fetal brain—The fetal Lipogenesis via Glycolysis-Abbreviated Citric acid Cycle (LGACC) is shown in the
The abbreviated citric acid cycle in tissues active in lipogenesis, is only speaking of the ultimate fate of each and such majority of glucose molecules being combusted in the above manner (though otherwise destined for a full-fledged citric acid cycle), and not of the whole scene of metabolic cycles/activity going on in the cell or it's mitochondria, because as a whole, there can be imperceptible merge of both path ways, as some full-fledged citric acid cycles are invariable in any cell.
The question that arises at this point is whether both citrate molecules generated from a single molecule of glucose are diverted to fatty acid synthesis, or one will continue into full citric acid cycle to generate needed ATP. Due to the sheer number of acetyl-CoA molecules needed for each molecule of cerebronic acid generated, it seems plausible that both citrate molecules are diverted into fatty acid synthesis that accounts for significant glucose/oxygen salvage. The economics of both glucose and oxygen (in absolute numbers) show dramatic difference if both citrate molecules are diverted to fatty acid (cerebronic acid) synthesis, as opposed to only one is diverted, the other being continued through the full-fledged citric acid cycle, generating ATP in the usual manner.
The ATP Yield Vs. O2/Glucose Expended in Either 1 Citrate Diversion, or 2 Citrate Diversion is Explained as Follows—
2-citrate diversion—in this process, 8 ATP are generated via glycolysis with 1 molecule of glucose (with 1O2 expended). So also, 6 ATP are generated when 2 acetyl-CoA molecules are formed (with 1O2 expended). The two citrate molecules will be cleaved to 2 molecules of oxaloacetate, and 2 molecules of acetyl-CoA in the cytosol by ATP-citrate lyase. The 2 acetyl-CoA molecules will participate in fatty acid synthesis, whereas the 2 molecules of oxaloacetate in the cytosol will be reduced to malate by 2 NADH+H+ (generated via glycolysis), as in the last steps of cytosolic malate shuttle. The 2 molecules of malate will return to mitochondria to form 2 molecules oxaloacetate through mitochondrial malate dehydrogenase. However, no ATP can be credited for this reaction of the last step of citric acid cycle, as the transformation of oxaloacetate to malate is accomplished by using the reducing equivalents generated in glycolysis, and as in a malate shuttle, the 6 ATP generated via the mitochondrial malate dehydrogenase are accounted to glycolysis, and not to the citric acid cycle. There is no complete revolution of the typical citric acid cycle that generates another molecule of malate. Accordingly, the total ATP generated in this process via glycolysis-citric acid cycle of 1 molecule of glucose is 14 (8 ATP from glycolysis, and 6 ATP during the formation of 2 acetyl-CoA), expending a total of 2 O2. For 1 molecule of cerebronic acid to be synthesized, the fetus spends 6 molecules of glucose (and 12 of acetyl-CoA), and 12 molecular O2, generating 84 ATP in the process (see table-4).
1-citrate diversion—in this process, one-citrate molecule continues into the full-fledged cycle to produce 12 additional ATP, with an over-all total of 26 ATP generated with 1 molecule of glucose, 4 oxygen being expended in the process. However, with a total of 12 glucose molecules needed for 1 molecule of cerebronic acid to be synthesized, the fetus is bound to spend 48 molecules of O2, however with 312 ATP generated (see table-4).
Table-4, Glucose/O2 spent vs. ATP generated via glycolysis-abbreviated citric acid cycle during the synthesis of 1 molecule of cerebronic acid—involving either 1 or 2 citrate diversion into FFA synthesis; and further comparison of ATP yield with full-fledged glycolysis-citric acid cycle
In the above table, with reference to 1-citrate diversion, 12/12 acetyl-CoA signifies that 12 of them are diverted to fatty acid synthesis, whereas 12 are continued into the full-fledged citric acid cycle.
With 1-Citrate Diversion, the Theoretically Probable Absolute Excess of Glucose/O2 Spent, and Excess ATP Generated, Compared to 2 Citrate Diversion, is—
Comparison with the full-fledged glycolysis-citric acid cycle—Comparing the above to the ATP gain/oxygen expenditure via the regular full-fledged glycolysis-citric acid cycle of a single glucose molecule (when 38 ATP are produced per 6O2), it can be noted that the yield per 1O2 is 6.3 ATP (6.3/1O2), whereas during 2-citrate diversion the yield per 1O2 is 7 ATP (7/1O2). This seems optimistic, because though glucose spent during fetal neuronal lipogenesis via 2-citrate diversion is 2.7 times more to generate similar ATP as the regular citric acid cycle (that is, 6 glucose generating 84 ATP vs. 1 glucose generating 38 ATP), the oxygen expenditure is lowered by 10% for similar ATP yield.
It can also be deduced that the D-glucose supplements enormously aid fetal brain development while the oxygen requirements are reduced by 10% for similar generation of ATP, whereas the absolute O2 requirement itself is reduced by 400% by the rapid anabolic process accomplished in a set unit time (time vs. achieved glucose supply/lipogenesis) by 2-citrate diversion (as in a well-fed state), wherein the absolute glucose requirements are also reduced by 200%. This deduction is of extreme significance when one can be concerned or skeptical about possible adverse effects of prevailing hypoxia in the setting of therapeutic D-glucose supplements. The 400+10% O2 salvage is apart from 33%+ of oxygen salvage achieved by curtailing beta oxidation of fats, and by preventing the fetal body muscle protein utilization for energy requirements (the ATP/O2 salvage being more from the latter). It may be noted that the activity of ATP-citrate lyase is increased during carbohydrate availability, induced by insulin.
The above numbers need additional comment. As was clarified above, following the combustion of a single molecule of glucose, the acetyl-CoA diverted to fatty acid synthesis is doubled in 2-citrate diversion, so that lipogenesis can be achieved rapidly and effectively with drastically less glucose/oxygen expenditure (in absolute numbers) even in the situations of relatively low glucose/oxygen availability. However, this is achieved at the expense of high number of ATP that could have been otherwise generated by 1-citrate diversion. Nevertheless, it may not be overlooked that the first and the foremost priority during fetal organogenesis is the lipogenesis needed in exponential amount in the rapidly developing fetal brain, and everything else must be concerted in that direction. However, for the sheer number of acetyl-CoA needed for glycolipid/phospholipid synthesis, ATP is being generated in significant numbers from glycolysis alone which path way is invariable for the needed acetyl-CoA, and in this unique context, the citric acid cycle, though esteemed for it's economics, is rather a wastage, and can be mostly by-passed. It also may be noted that the fetal brain compensates for the absolute number of ATP lost via lipogenesis by the exceeding amount of glycolysis, but spending less of oxygen, and more of D-glucose, which is supplied in this therapeutic endeavor. It also follows that the fetus can engage in some of the full-fledged citric acid cycles only when the ATP requirements within the brain are more (that is, it relays in the brain's energy vs. growth requirements).
The Energy Versus Growth Requirements within the Fetal Brain—
Fetal growth and maturation—The fetal brain's growth requirements are enormous, whereas energy requirements are substantially less compared to it's adult counterpart. It merely means to say that the fetal brain is quiescent, but not inert. Only it's heart can surpass the brain in the amount of ongoing functional activity in quantity and quality, needed for continued survival in it's unpredictable aquatic environment. The brain's sympathetic and parasympathetic circuits are very active even at this stage, as the heart rate should respond by beat to beat variation to the hypoxic insults, or to the hypotensive episodes, the input carried by para-sympathetic afferent. Hence, the brain's neuro-transmitters must be synthesized extremely rapidly. The fetal heart rate being double that of an adult, the brain's basal sympathetic out flow is also very active and very rapid. The fetus in addition has very potent brain-endocrine system, the hypothalamo-pitutary axis being functional from very early on, that controls the adrenals, the thyroid, and the gonads, in terms of both growth and function. While such growth is unsurpassed, the brain's cortical functional activity, and the activity of the neuronal circuits essential for volitional motor activity are minimal, making it's ATP requirements far less in comparison to the growth requirements. It can be aptly said that the fetus with it's uncomparable growth potential, is not only a feeding larva, but also a resting pupa, and there needs to be a very fine balance achieved between it's growth and it's gain of ATP.
Because a sheer number of acetyl-CoA units are needed/produced for fetal brain development, and the process being also accompanied by moderate ATP yield that is proportional to the normally low fetal activity/energy requirements, it is prudent to say that the abbreviated citric acid cycle with predominant 2-citrate diversion is the main path way, and the full-fledged citric acid cycle (with more glucose-oxygen expenditure with high ATP yield) as needed, being the additional path way in the fetal brain. As per the popular belief some full-fledged citric acid cycles are invariable, one reason among the few being—for the end products of protein break down to merge in the cycle, as there is active amino acid metabolism also in the brain (where there is seemingly only of glucose trafficking, and of lipid manufacturing) for the synthesis, and for the rapid turn-over of multitude of neurotransmitters like—GABA, epinephrine, norepinephrine, acetylcholine, dopamine etc. The earlier discussion was about the merits of 2 citrate vs. 1 citrate diversion into lipogenesis, but the significant amount of ATP consumed later for lipogenesis itself is unchanged, starting from citrate cleavage. All the anabolic processes are energy consuming. During the nine months of fetal intrauterine stay of which pregnancy is about, most of the energy is deservingly devoted for such anabolic needs.
What Makes the Glycolysis—Abbreviated Citric Acid Cycle in the Fetal Tissues Engaged in Lipogenesis a Possibility, and Yet Generates any ATP at all—
It can be said that the citric acid cycle is an ultimate testament of the body's achievement in efficiency and economy. However, a substantial number of glucose molecules after glycolysis can by-pass the full-fledged cycle, as long as the concerned reducing equivalent (the 2H+ or protons) generated via the glycolytic process are connected to the mitochondrial respiratory chain at least through one step of the citric acid cycle to generate ATP. Thus it is obvious that no glucose molecule can short-cut or by-pass any of the steps of glycolysis, whereas by-passing and short-circuiting with ease can be done to the many steps of citric acid cycle, and yet generate ATP. In the case of glycolysis-abbreviated citric acid cycle, the step involving glyceraldehyde 3-phosphate dehydrogenase of glycolysis is connected to mitochondrial respiratory chain through the last step of citric acid cycle (involving mitochondrial malate dehydrogenase) through maneuvers similar to the malate shuttle, and the subsequent step involving the pyruvate dehydrogenase complex being mitochondrial, is directly connected to the mitochondrial respiratory chain. Full-fledged citric acid cycle is geared towards maximal efficiency of glucose combustion, but by all means it's many steps though not all steps, can be by-passed. So it can be clearly stated that the abbreviated citric acid cycle that many glucose molecules must pursue is fully compatible with cell function in the sites of active lipogenesis in-utero. It is also compatible with sufficient ATP production even while only 14 ATP are being produced with each abbreviated cycle, as it's sheer number accounts to a substantial total.
Is predominant abbreviated citric acid cycle (ACC) compatible with optimal cell function ? This question can be answered by critically examining the intermediates of the citric acid cycle. The most important of these are citrate, malate, α-ketoglutarate, and the succinyl-CoA that are intimately and essentially connected to other vital metabolic path ways. In the ACC, the citrate and the malate are the target intermediates, and hence the focus can be diverted to the other two. The α-ketoglutarate is essential for protein metabolism, for it's pivotal role involving the deamination of many of the α-amino acids. The brain cells also need it for such process, for the many activities that go on in the brain involving the amino acid metabolism. The Dopamine, the epinephrine, and the norepinephrine are synthesized in the brain from tyrosine, but are metabolized with no involvement of α-ketoglutarate. GABA is synthesized from L-glutamate, and it's metabolism in the brain involves the need of α-ketoglutarate. The succinyl-CoA is essential for heme synthesis, but obviously it's need is more in the erythropoitic tissues, and not necessarily in the sites active in lipogenesis.
In the tissues specializing in lipogenesis, such function predominates, and the cell is capable of controlling it's own ATP production only as needed, and no more.
1. The steps involving combustion of food stuffs, and of the flow of reducing equivalents in the respiratory chain of mitochondria for oxidative phosphorylation are step-wise, allosterically controlled and efficient, rather than explosive or wasteful (Mayes P A).
2. In the mitochondria, the oxidation and phosphorylation are tightly coupled (Mayes P A). That means, with out the availability of ADP for phosphorylation, the oxidation expending molecular oxygen can not proceed. The availability of ADP is in turn controlled by the body's utilization of ATP, thus reducing it to ADP. Essentially, when there is adequate availability of ATP within the cell for needed biochemical activities, and no more ATP is needed (as can be evident by the relative unavailability of ADP within the cell), no more of it is produced in the mitochondria.
3. The function of ADP/ATP transporter which permits entry of cytosolic ADP into, and the ATP out of mitochondria is rate limiting. The overall rate of a simple or complex series of biologic reactions is determined by the slowest step in such series which is rate limiting to the entire series (Guyton A C). Under a resting condition as the fetus is, the concentration of ADP in the cells is very low, and the chemical reactions that depend on ADP, the most important being oxidative phosphorylation with ADP as it's substrate, can be slow also, thus ADP being the rate limiting factor for all energy/ATP producing metabolic pathways of the body.
4. Insulin, increased during glucose availability and satisfied ATP needs (a scenario helped by D-glucose supplements) stimulates lipogenesis in the fetus, the most important effect being increasing the activity of acetyl-CoA carboxylase needed for synthesis of melonyl-CoA, the building block of fatty acids. Such diversion curtails the citrate continuity into the citric acid cycle, that in turn prevents oxidative phosphorylation.
5. The fatty acid synthase complex, and the acetyl-CoA carboxylase are the enzymes unique for their ability to adapt to the body's immediate requirements. Insulin increased during glucose availability and hence satisfied ATP needs (a scenario helped by D-glucose supplements) also plays a role in inducing the gene expression of these enzymes, and thus causing their biosynthesis. This enhances the fetal brain's anabolic process, and prevents the ATP generating catabolic path ways.
6. The activity of ATP-citrate lyase is increased during carbohydrate availability, and decreased during it's lack. It is also induced by insulin. This state of affairs enhances lipid anabolism, and diminishes the glucose/citrate catabolism (a scenario also helped by D-glucose supplements).
Serine needed for the phospholipid/glycolipid synthesis is synthesized by the intermediate of glycolysis—Serine, the only amino acid needed for brain phospholipids/glycolipids is synthesized by 3-phosphoglycerate, the intermediate of glycolysis. Thus the predominant glycolysis-abbreviated citric acid cycle in the fetal brain is self-sufficient in generating also other elements needed for fetal brain development. One glucose molecule is utilized for generating 2 molecules of serine. This adds one more molecule of glucose expended for 2 molecules of brain ceramide synthesized.
At this point, after analyzing the tremendous amount of fatty acid ‘lay over’ that is to be rapidly accomplished in the fetal brain during the last months of it's life in utero, it is also a legitimate issue to discuss if the fetus must solely engage in it's fatty acid synthesis, or if there is significant placental transfer of maternal fatty acids to be incorporated to form the longer chain fatty acids of the brain, or the adipose tissue triglycerides, and if so, by what proportion? The answer seems to be difficult. As was mentioned, the free fatty acid (FFA) transfer across the placenta is by simple diffusion as per the concentration gradient, and is compounded by the fact that there are no cellular components on the maternal part of the placenta, the whole maternal compartment being pools of blood, whereas the fetal side is made of only the syncytio-cyto-trophoblast and the fetal vessel wall that the fatty acids have to maneuver through. This anatomical ease accomplishes significant fatty acid transfer needed for the human fetus, whose lipid lay-over in the brain is significant for it's voluminous size to be ultimately achieved. The immediate fatty acid anabolic ‘lay over’ in needed sites probably also accounts for the fetus maintaining lower FFA concentration contributing to higher gradient for continued simple diffusion through the placental interface. Such rapid fetal lipogenesis is in contrast to heightened maternal lipolysis coinciding with such time, to maintain ongoing high maternal-fetal FFA concentration gradient/transfer.
There is support for such theoretical ease of placental fatty acid transfer. It was demonstrated directly in the sheep (Van Duyne et al, 1960). When radioactive fatty acids were injected intravenously into the mother, they appeared in fetal circulation in few minutes. It can also be confirmed by the observation that the essential fatty acids were found in the adipose tissues of the new born infants (Bagdade and Hirsh, 1966
It was hypothesized by past researchers, that the fatty acid composition of fetal adipose tissue shows that the synthesis de novo assumes greater significance in the later part in-utero. This was evidenced by the fact that towards the end of fetal life, the proportion of linoleic acid (an essential amino acid to be supplied by the mother) in the fetal adipose tissue decreases, and the proportion of palmitic acid (that can be synthesized by the fetus from acetyl-CoA via melonyl-CoA path way) increases, and at birth, the adipose tissue of the neonate contains only one tenth of linoleic acid, and twice the amount of palmitic acid compared to the adipose tissue of the adult. Accordingly it was hypothesized that synthesis de novo assumes greater significance, which was thought to be further supported by the fact that such fatty acid composition of the neonate closely resembles that of animals fed with high carbohydrate, and poor fat diet (N. B. Myant).
The above observations and conclusions by past researchers may infer that there can be predominant de novo fatty acid synthesis by the fetus at term, but it may not necessarily represent the specified proportion, in the manner implied. It is due to the following reasons, as put forth by the author inventor, validated by laws governing the kinetics of diffusion. Palmitic acid is synthesized by the fetus, and linoleic acid is not, but it does not rule out or clearly quantify how much palmitic acid is also supplied by the mother. The non-essential fatty acids are transferred also across the placenta, just like the essential fatty acids, without any differentiation (Leslie Myatt). It also does not rule out more of palmitic acid transfer. Maternal lipogenesis increases in linear fashion to a maximum at 25 weeks, when it continues as a plateau to term. Maternal lipolysis predominates in the later part of pregnancy, when there is ongoing de-esterification, and of fat mobilization from the past-laid maternal fat depots, by the action of HPL. It can raise the circulating maternal free palmitic acid level that can cross the placenta by diffusion, through concentration gradient. The FFA levels reach a maximum of 4-5 times of non-pregnant levels in the later part of pregnancy. At 37-40 weeks of gestation, the maternal FFA levels increase exponentially by 60%. In an adult on balanced diet (like a pregnant woman), the adipose tissue subcutaneous fat contains oleic acid 47% (18 carbon mono-unsaturated fatty acid), palmitic acid 20% (16 carbon saturated fatty acid), and linoleic acid 11% (18 carbon unsaturated fatty acid). The adipose tissue of new born infant contains palmitic acid as 40%, oleic acid 25%, and linoleic acid 1% (Hirsch, 1965). The fatty acids pass through the lipid bilayer of cell membrane by simple diffusion, and as per the kinetics of diffusion, with the diffusion rate being inversely proportional to the molecular weight of a molecule, it is possible that though the 18-carbon unit oleic acid is present in higher concentration in the maternal fat depots and in the maternal blood, it's diffusion across the placenta must be slower, compared to that of the 16-carbon unit palmitic acid with lesser molecular weight and smaller chain length, which after entering the fetus can be directly laid down to form the triglyceride molecules of the fetal sub-cutaneous adipose tissues. The proportion of linoleic acid in maternal plasma is lower, and in addition, it's molecular weight is higher, and the chain length longer than that of the more predominant palmitic acid.
It can be reasonably concluded that in a normal fetus the significant amounts of the maternal fatty acids are mostly laid down in the manner transferred from the placenta, and the fetus need not synthesize all that is required. Manipulation of maternal diet can also proportionally increase such transfer. Above all, as discussed, nature's device of maternal lipolysis through HPL of pregnancy is important and purposeful, as such scheme is also coupled with maternal utilization of FFA instead of glucose for energy, as the latter also needs to be diverted to the fetus. It also is worth noting that maternal high carbohydrate diet/circulating glucose can generate more triglycerides of her adipose tissues than the high fat diet (though the latter can directly contribute to the rise of circulating FFA in the maternal blood to be used as her fuel), most of the maternal tissues being resistant to insulin effects, whereas her fat depots and the placenta are not.
Maternal D-Glucose Supplements can Substitute for/Correct the Fetal Oxygen Lack Via Maternal Lipogenesis/Lipolysis, Resulting in ‘Ready-Made FFA’ Transfer—
It is clear from the foregoing paragraph that the maternal glucose is the raw material for the maternal fat depots from early on in pregnancy that is mobilized later on when the fetal demands are more in it's phase of lipogenesis. It signifies the needed maternal circulating carbohydrate (by IV or dietery supplements) as the indirect element (as maternal FFA) to be incorporated during fetal lipogenesis, and as the direct element of optimal maternally derived circulating glucose in the fetus that also engages in de novo lipogenesis. That means, the mother synthesizes FFA to transfer them ‘ready-made’ when the fetus is in it's ‘speed mode’ of lipogenesis later on, obviating a tremendous need of glucose/oxygen by the fetus. At the conclusion, it is worth stressing that D-glucose substitutes for O2 lack, with an oxygen salvage in the fetal brain as—(a) 400% of absolute oxygen salvage by 2-citrate diversion (instead of one) during sufficient glucose availability, for the rapidly accomplished fetal neuronal lipogenesis (or lipogenesis in general), and an additional 10% ATP/oxygen salvage through LGACC; (b) 33% by obviating the brain's utilization of FFA as fuel; (c) >33% by preventing ATP expending amino acid utilization which in turn needs more of full-fledged glucose/O2 expending citric acid cycles also; (d) fetal gain of predominantly D-glucose-derived maternal FFA, thus obviating an otherwise exceeding fetal need of ATP/O2. Such deduction helps to alleviate one's possible concern that hypertonic D-glucose supplements seem disproportionately high compared to the amount of oxygen the fetus can avail. The glucose needed in this context is indeed disproportionately high in the rapid fetal lipogenesis compared to the oxygen needed, the glucose expenditure being 2.7 times more, but the oxygen needed for the same amount of ATP synthesis is 10% less than what is spent by the tissues elsewhere.
It was sufficiently stressed on multiple occasions how the citric acid cycle of the D-glucose metabolism is life sustaining through it's pivotal role in ATP production. During fetal hypoglycemia and hypoxia citric acid cycle will cease to be operative, and the D-glucose supplements improve not only fetal hypoglycemia but also fetal hypoxia to a significant extent as clearly evidenced by the foregoing objective data. It is also sufficiently clear that no biological function can ever happen without ATP in the fetus, and that the lack of ATP by the cessation of citric acid cycle can culminate in death, and lack of glucose can culminate in the cessation of the citric acid cycle. As a translation of what is herein deduced, it can be stated—for the fetus in-utero ‘glucose is life’, and life is being given to the fetus by it's supplements.
Acquisition of fat in the subcutaneous adipose tissues of the fetus in the later months of pregnancy has multiplicity of purposes: physiological awakening of thermoregulation soon after birth to meet the unpredictable temperature fluctuations ex-utero, and the heat required being provided by the adipose tissue; the relative fetal hypoglycemia due to abrupt cut off of maternal provisions, and explosion of physical activity in all parts of the newborn including vigorous crying, such an absolutely vital activity in high tempo at birth and after needing tremendous energy, and the neonate left to be solely relying on burning it's fat stores.
With the subcutaneous fat depots being sub-optimal, a significantly deprived IUGR baby devoid of baby-fat appears like a ‘little adult’ with a typical ‘wizened look’ which is not hard to discern.
The amount of glucose needed for the adipose tissue lipogenesis can be comprehended by acknowledging the fact that one molecule of triglyceride (TGD) is formed by the esterification of one molecule of glycerol with three molecules of free fatty acids. A new born infant has predominantly 16-carbon atoms palmitic acid (40%), or 18-carbon atoms oleic acid (25%) in it's subcutaneous tissues. Accordingly, the three molecules of free fatty acids in the fat depot TGD need 24-27 acetyl-CoA or 12-13.5 glucose molecules, and inclusive of the ½ molecule of glucose needed for glycerol synthesis, just one TGD molecule needs 12.5-14 of glucose molecules in it's formation. Based on such high toll on the available glucose, it seems that even in normal fetus, acquisition of FFA from the maternal compartment is invariable addition to fetal de novo synthesis. It was already noted that glucose expenditure in absolute amount is curtailed by 200%, and the absolute oxygen needed during exclusive fetal lipogenesis is 400%+10% less, and such saving provision is applicable to the lipogenesis in the subcutaneous adipose tissues also, that is strongly in favor of therapeutic D-glucose supplements.
It seems rather phenomenal that the fetal umbilical vein alone can supply all the needed oxygen for the enormous growth accomplished by the fetus through a mere span of ten lunar months. It makes one contemplate that there must be other source(s) so far not suspected. The fetal aquatic environment can be such source. It seems against nature's intension that the amniotic fluid being the sole fetal world can be a dormant environment, rather than an active contributor to the fetal growth and maturation in every possible manner. After all, the endless oceans can accommodate enough oxygen to support it's vast aquatic life, and it is a testament to the fact that water is a satisfactory carrier of oxygen, as our focus of interest at this point is towards the myometrial and decidual interstitial fluid as a suitable milieu for oxygen transit, though through a short span of distance. The extracellular water of the vertebrates and the primate humans is known to be similar to the electrolyte composition of the waters of the oceans (Goldberger E, 1980), such biological property reflective of the vast nature preserved through billion years. Additionally, it was already confirmed by past researchers that AF does contribute to, and is essential for optimal fetal growth. It was also observed that the PCO2 of the AF is very high (R. Lisle Gadd, 1970, and Nicolaides et al 1989), probably in the range of 48 mm/Hg (Rooth et al), mostly due to the virtue of it's high solubility/diffusion coefficient. To substantiate the fact that AF can be a significant source of fetal oxygen supply, it is important to understand the dynamics of oxygen and CO2 carriage in the pregnant/non-pregnant systemic circulation, their release at the level of placental intervillous space/tissue capillaries, along with the dynamics of the partial pressures of oxygen/CO2 at these sites. The complex biological principles of the terrestrial lifeforms are geared towards more efficiency of oxygen carriage/supply, by virtue of it's natural gaseous existence in the lungs than as per it's existence in lowered proportion in the aqueous ecosystem of the oceans. How ever, the fetal activity in it's fluid world in solitude is after all far less than that of the innumerable aquatic forms of the oceans, restlessly in motion, yet gaining their fair share of oxygen.
The pulmonary gaseous exchange in a healthy adult—the partial pressure of oxygen (PO2) in the alveoli is 104 mm/Hg. The pulmonary blood equilibrates well with the alveolar gases, and hence the purified blood leaving the lungs also has the same PO2 of 104 mm/Hg. However, after it is joined by the bronchial venous blood, it is reduced to 95 mm/Hg. Hence, essentially the systemic arteries terminating into the arterioles and capillaries have the same PO2 of 95 mm/Hg.
The gaseous exchange at the interstitial spaces in a healthy adult—at the tissue interstitial spaces the PO2 is 40 mm/Hg with effective filtration gradient of 55 mm/Hg at the arterial capillary level. The capillary and venous blood PO2 equilibrate effectively with that of tissue interstitial space, and accordingly, the venous blood leaving the tissues has PO2 of 40 mm/Hg. In fact, in the interstitial spaces the PO2 could be more, when the rate of blood flow is increased. The blood flow, if increased by 400%, as of the muscle during muscular exercise, the PO2 in the interstitial fluid can increase from 40 to 66 mm/Hg, and a maximum of even 95 mm/Hg can be achieved by markedly increased blood flow (Guyton A C). The uterine tissues during pregnancy with significantly increased vasculature, and exceeding metabolic activity can attain higher interstitial fluid PO2, which however, was not explored as a targeted issue by past researchers.
Diffusion at the intervillous spaces where the fetal umbilical vessels terminate—the uterine artery has a PO2 of 95 mm/Hg. However, due to the sinusoidal architecture of the maternal placental compartment conforming to an arteriovenous shunt, the PO2 of the uterine spiral arteries fall to a level of 30-35 mm/Hg in the sinusoidal spaces (Pritchard J A. et al) (however, in the uterine vein, the PO2 again raises back to 40 mm/Hg, as in the rest of the maternal systemic venous circulation, overcoming the placental shunt effect). The foregoing set of numbers, and other similar data that follows, are shown in table-5.
The fetal umbilical artery (carrying fetal deoxygenated blood) has a PO2 of 15 mm/Hg which after exchange with the maternal blood rises to only 27 mm/Hg in the umbilical vein (carrying fetal oxygenated blood). The Bohr effect can be summated as—‘the hemoglobin-oxygen binding affinity is inversely proportional to the it ion concentration, and also to that of the CO2 concentration’. Accordingly, in the placental sinusoids there is shift to the left of fetal oxygen-hemoglobin dissociation/association curve (such shift being a reflection of higher O2-hemoglobin affinity or association) due to: (a) and (b) effectuated by Bohr effect that can be described as—(a) low PCO2 of the sinusoids to start with (due to maternal hyperventilation) causing net higher diffusion of CO2 (whose diffusion coefficient is 20 times that of O2) from fetal blood, thus reducing the CO2 of the fetal blood proportionally; (b) fetal blood becoming more alkaline as a result of (a); the (a) and (b) resulting from Bohr effect further aided by (c) low affinity of fetal hemoglobin to 2,3-DPG (2,3-diphosphoglycerate) (the 2,3-DPG causes stability of deoxyhemoglobin). Due to left-ward shift of fetal hemoglobin-oxygen dissociation/association curve in the placental sinusoids due to (a), (b), and (c), the fetal hemoglobin can carry more oxygen even at a low PO2 of maternal sinusoids.
However, based on the plotting of oxygen-hemoglobin dissociation/association curve that is sigmoid, due to the prevailing low PO2 in the sinusoids, despite the shift to the left of the oxygen dissociation/association curve, the fetal hemoglobin oxygen saturation will be only 68% (Longo 1972), and not 97% (the saturation of hemoglobin in the lungs), as the PO2 of 30-35 mm/Hg in the sinusoidal spaces does not correlate with the plateau of the oxygen-hemoglobin dissociation/association curve in the manner the plateau of the oxygen-hemoglobin dissociation/association curve correlates at the alveolar spaces with the PO2 of the alveoli as high as 104 mm/Hg, facilitating maximum hemoglobin saturation. However, this low PO2 of 27 mm/Hg of the fetal arterial blood is still effective for the reason that only 5 mm/Hg of PO2 is sufficient to support the oxidative metabolic function of the cell, as a function of cytochrome oxidase (Rodwell V W et al).
The PCO2 of the umbilical vessels show interesting values. The umbilical artery carrying fetal impure blood has PCO2 of 48 mm/Hg, and the umbilical vein carrying the fetal oxygenated blood has a PCO2 of 43 mm/Hg. The uterine artery PCO2 is 32 mm/Hg during pregnancy due to maternal hyperventilation, and after an exchange with the fetal blood, it increases in the intervillous space to an average value of 38 mm/Hg.
As shown in table-5, the above equilibrated PCO2 values of placental exchange show a marked difference from the equilibrated values of the systemic circulation of the non-pregnant controls, where the PCO2 of the venous blood indeed equilibrates to 45 mm/Hg of the interstitial fluid, and the pulmonary deoxygenated blood is also equilibrated with that of the alveolar air, the latter happening normally with in a fraction of a millimeter, and within the ⅓rd transit time of the pulmonary capillary blood (Guyton A C). It is due to the high diffusion coefficient of CO2, and because of the fact that the PO2 in the alveoli being very high, falling in the plateau range of the O2 association (thus maximizing the Haldane effect of CO2 release). At the placental level, the explanation is not as easy or straight forward, for the equilibration that is seemingly not attained. The umbilical vein PCO2 seems to have not equilibrated with the maternal sinusoidal PCO2 despite high diffusion coefficient of CO2, and a lower prevailing maternal sinusoidal PCO2, a more suitable milieu than that of the capillary end of the systemic circulation. In fact, there is no valid biochemical/physiological explanation to put forth, for failure of the umbilical vein PCO2 to be lowered, as expected. But the situation may not be what it seems as. Due to very high diffusion coefficient of CO2, the amniotic fluid (AF) PCO2 probably attains very high values of 48 mm/Hg, as observed by the past researchers, and due to it's instantaneous diffusion even through tissue planes, it may equilibrate easily with the PCO2 of the traversing umbilical vein making it higher than the previously equilibrated lower levels after an exchange with the maternal blood at the intervillous space. Because of it's volatility and high diffusion coefficient, the CO2 diffusion from
the AF into the cord blood can be instantaneous. The AF water diffusion is 50 ml/hour into the cord blood, during the mid/late pregnancy (Plentil 1961). It is significant to note that the diffusion capacity of CO2 across the alveolar membrane, for long had not been measured, as the diffusion is instantaneous, and the difference across being immeasurable.
Studies of acid base status of amniotic fluid (AF) was published by Rooth, Sjostedt, and Caligara (1961). They concluded that the pH and the CO2 tension in the AF reflect corresponding values of the umbilical artery (in the range of 45-60 mm/Hg), and those of the fetal subcutaneous tissues, and that towards the end of pregnancy there is significant increase in the carbon dioxide tension of AF from 51 to 58 mm/Hg. Lower numbers were indicated in their later studies, though the exact numbers were not specified. It is questionable whether these observations of AF are the cause or effect of what are reflected in the umbilical artery, and in the fetal subcutaneous tissues. It is most plausible they are the cause. Except for fetal urine, there is no fetal contribution to the AF later in pregnancy, and it's chemistry and volume are mainly a result of exchange with the maternal extracellular fluid, the AF being replaced every 3 hours. Accordingly, if the umbilical artery and the fetal subcutaneous tissues show similar pH and PCO2 values as those of AF, it is due to the rapid diffusion of CO2 from the AF into the fetal tissues and the umbilical cord, proportionally raising the values both in the umbilical artery and the vein. Even if the normal fetus generates more of CO2, there is no physiological means of how it is reflected in the AF, except through fetal urine that CO2 is not a constituent of. Hence it is most plausible that the CO2 from the AF has diffused incessantly into the umbilical cord, and also into the fetal subcutaneous tissues, it's original source being the uterine myometrium itself that surrounds the whole of the non-placental amnion.
It was previously discussed that the AF content of CO2 can be very high, especially in oligiohydromnios. It is highly critical to explore how the CO2 of the AF has attained such high value despite the low maternal PCO2 of 40 mm/Hg in the uterine vein (45 in non-pregnant controls), and 32 mm/Hg in the uterine artery (lower than non-pregnant value of 40) and 38 mm/Hg in the placental intervillous space. The explanation can be as follows—The CO2 is mainly the product of carbohydrate metabolism, especially of the citric acid cycle. The citric acid cycle is deemed to be very active in rapidly enlarging uterus all through pregnancy. Though the essential amino acids needed for protein synthesis are required to be supplied from the maternal diet, most of the non-essential amino acids can be synthesized by the mother from carbohydrate sources. Alanine and hydroxyproline are synthesized from pyruvate; glutamate and glutamine that make up the largest amino acid pool of the body are intimately associated with, and are synthesized from α-ketoglutarate during transamination of α-ketoglutarate. Aspertate and aspergine are formed from oxaloacetate; serine is derived from 3-phosphoglycerate; and glycine formed from glyoxalate. The uterus enlarges 16 times in weight at term from it's non-pregnant state. This is mostly through hypertrophy (enlargement of the diameter/length of individual muscle fiber), and very less through hyperplasia (increase in the number of muscle fibers). There is great expansion of sarcoplasm of the enlarged muscle cells that store ATP, glycogen (synthesis of which needs significant number of ATP), and creatine phosphate that also stores ATP in an alternate form in the muscle. When proteins are synthesized, large portions of ATP are also used to form the peptide linkages that store energy in the linkages. These indicate that there must be very actively ongoing citric acid cycle in the uterine musculature for the generation of needed amino acids, and the needed ATP. There is evidence that there is enormous proliferation of mitochondria in each cell, for needed ATP production, and for ongoing glucose combustion. In a virtual uterine protein anabolic process, just as the lipid anabolic process of lipogenesis, the carbohydrate catabolic process is intertwined. It increases the CO2 generated by exponential amounts in the proliferating uterine musculature/decidua that can immediately diffuse into the adjacent AF. As the diffusion of the gas is directly proportional to the diameter of the space it diffuses into, it will be more into the amniotic cavity (with very high transverse and longitudinal diameter) rather than the uterine venous capillaries. This localized rise of CO2 in the enlarging uterine interstitium can happen, despite the low CO2 tension elsewhere in the maternal body. The amniotic cavity being a low resistant high volume chamber, and the solubility coefficient of CO2 being very high (that is, CO2 is physically and chemically attracted to the water molecule), the CO2 diffusion that is instantaneous through any of the tissue planes (including the amnion), can be significant towards the AF, than into the uterine venous circulation.
(As an alternative, dissociation of urea [NH2—CO—NH2] of the AF to CO2 can be thought of, though it will raise toxic ammonia levels of AF which the fetus has to swallow. The fetal liver is capable of handling ammonia again entering through the gut, by reformation of urea. However, the biochemical support for urea dissociation (into ammonia) after it is formed is not found. Despite long standing uremia in an end stage renal disease, only blood urates, hippurates, indoles, benzoates, phenols, and polyamines are normally found to be elevated, but not the ammonia.)
It may be noted that the uterine vein PCO2 is 40 mm/Hg, whereas it is only 38 mm/Hg in the placental intervillous space (most probably the equilibrated value, such equilibration being instantaneous for CO2). It indicates that there is definite higher non-placental myometrial contribution of CO2 to the uterine vein which implies that myometrial interstitial PCO2 must be greater than 40 mm/Hg to start with, that later equilibrated to 40 mm/Hg, joining with the intervillous blood as it drains into the uterine vein. Such PCO2 greater than 40 mm/Hg in the myometrial interstitium is almost reaching non-pregnant values. In essence, the myometrial production of CO2 is far greater than the fetal, despite a predominant carbohydrate metabolism in the latter.
The ultramicroscopic structure of the amnion demonstrates that there are significant intracellular and complex intercellular canalicular system all through the layers that transmit fluid from the maternal interstitial compartment to the amniotic cavity. However, there is selectivity, as AF does not truly represent all the constituents of maternal interstitial fluid. Yet the respiratory gases of interest follow the laws of gaseous diffusion in the same manner: (1) in a gaseous mixture, (2) as dissolved gases in a solution, or (3) when changing from gaseous phase into a dissolved state in liquids. Paradoxically, the cell membrane is even less restrictive than the liquid barrier for the passage of the respiratory gases (Guyton A C).
And due to the avascular nature of the amnion, the PCO2 of the interstitial fluid, and not the arterial capillary end, is relied on. It can be stated that through the traversing transcellular and intercellular canalicular system of the amnion, there is a continuum of the uterine interstitial fluid, of which the respiratory gases are part of. And if there is an occasional cell membrane intervening, it poses no bather to either O2 or CO2. The following laws of net gaseous diffusion into a chamber (Guyton A C) are herein applicable. The amniotic cavity in this instance can be considered as a closed fluid chamber amenable to similar laws of gaseous diffusion—
1. Greater the pressure difference (P1−P2) across, greater will be the diffusion (Henry's law of solubility coefficient of gases), that is, the diffusion is from higher to lower pressure, P1 and P2 being the involved higher and lower pressures respectively.
2. Greater the solubility of a gas (S), greater will be the diffusion (Henry's law of solubility coefficient of gas).
3. Greater the cross-sectional area (A) of the chamber of diffusion, greater is the diffusion.
4. Greater the molecular weight of the gas (MW), lesser will be the diffusion, that is, the rate of diffusion is inversely proportional to the square root of it's molecular weight (Graham's law of gaseous diffusion).
Based on the above laws of gaseous diffusion, the net diffusion of CO2 is 20 times that of O2, because of it's very high solubility coefficient (S) that makes a gas to be chemically and physically more attracted to it's solvent, in this case, the water molecule. Accordingly, it is not a surprise, nor it is unexplainable, if the AF content of CO2 has been found to be very high.
The uterine myometrium being the source of the high AF CO2 content is further supported by the fact that in IUGR, the AF was found to contain exceedingly high amounts of CO2 (as was documented by Nicolaides et al, 1989), but as per the foregoing biochemical discussion in the previous sections, it is very obvious that in IUGR, the fetus is deprived of both glucose and O2, the invariable elements needed for CO2 production, and anaerobic glycolysis generates no CO2. Hence the source of AF CO2 can be only the myometrium, and never an IUGR fetus, though fetal oliguria can concentrate it within the AF (see the section ‘Fetal oliguria and oligohydromnios’).
The Possible Oxygen Diffusion into the AF
The above deduction undoubtedly proves the possible high CO2 diffusion from maternal extracellular spaces into AF. As it's rise in the AF is not subtle, due to it's high solubility/high diffusion coefficient, and was well documented, though the source was not explored being implied as fetal (Gadd R L, 1970; and Nicolaides et al, 1989), it nevertheless gives room to contemplate such possibility with oxygen diffusion also, though not with the same ease or of proportion. It was already mentioned that the interstitial fluid PO2 can approach a maximum of 95 mm/Hg, if there is significant increase in the rate of blood flow, and of the metabolic activity of the organ (Guyton A C), and both are inevitable during pregnancy. The blood flow is augmented in exceeding proportions because of the shunt effect of the placenta that decreases the peripheral resistance markedly in the uterine artery and it's tributaries supplying the whole of the uterus. It follows that the PO2 of the interstitial compartment of pregnant uterus can be higher than 40 mm/Hg (the value of interstitial PO2 elsewhere), and it is evidently much higher than the PO2 of the placental sinusoids. Though historically the amnion overlying the placenta is considered as the significant contributor to the volume and to the contents of the AF, as far as oxygen diffusion is concerned, the non-placental uterine area conforms to a source of higher oxygen diffusion secondary to higher PO2, and as a result higher net diffusion gradient into the non-placental interstitial uterine compartment, and then into the AF (further aided by the benefit of the in-vicinity placental shunt effect that actually pulls the blood from the uterine artery, and the systemic circulation).
Based on the Above Formula of the Rate of Net Diffusion of a Gas, the Following Observations for the diffusion of O2 into AF can be made—
1. The PO2 of the uterine interstitial fluid can be higher during pregnancy, in areas surrounding the non-placental amnion. This is in contrast to the low oxygen pressure in the AF itself. This will increase the net diffusion, due to increased pressure gradient of oxygen (P1−P2) across the amnion channels. The selectivity of the amnion may not be applicable to the gases of biological interest, and to the laws of gaseous diffusion universally governing the kinetics of gaseous diffusion, either through solids or fluids, and either into gaseous or fluid compartments/chambers.
2. The cross-sectional area (A) of the amniotic cavity (either longitudinal or transverse), configured as a chamber, is also very high, thus increasing the rate of diffusion of O2.
3. The molecular weight (MV) of O2 is low (32). This is inversely proportional to the rate of diffusion. With regard to free molecules not attached to others (O2 is free molecule; in CO2, it is physically attached to carbon), linear movement at high velocity is possible (Guyton A C).
4. With regard to the distance of the gas to be traveled, in this context, the area of importance is the AF very adjacent to the uterine wall itself where the fetal face and the oral area are located, and the fetal swallowing is effectuated. It is the narrower and the highly vascular lower uterine segment in the cephalic presentation. Hence, the distance needed to travel by the molecular oxygen is very less. Obviously, as the oxygen travels towards the center of the amniotic cavity, it's effective AF concentration probably diminishes due to the factor of dilution. Even after engagement, until the descent during labor when it touches the pelvic floor, deflexed attitude of the fetal head is prevalent which makes it's facial approximation with the uterine wall more feasible. This causes the fetal swallowing of AF with higher O2 content, before the gas is diffused.
Even after the descent and flexion of the fetal head, in the commonly prevailing left occipito-anterior position, due to the high concavity of the sacrum and the similar curvature the uterus tends to maintain below the pelvic inlet during labor, the fetal oral area will be still facing the concavity of the posterior wall of the pelvic cavity below the overhanging promontory of the sacrum, making the fetus swallow the AF very close to the uterine wall. It can be further said that the neonatal rooting reflex (so strongly prevalent in the neonates, and is most basic for their instinctive acts meant for cooperatively seeking the maternal breast, suckling, swallowing, and survival) was sufficiently rehearsed by the fetus in-utero, making it reflexively turn it's head towards that side, whenever the uterine wall/AF motion touches it's either cheek (by maternal position or movement). This helps the mechanism of fetal swallowing taking advantage of the uterine disposition that is closest to it's cephalic orientation, even in complete head-flexed attitude. It obviously facilitates the fetus swallow more of oxygen and the solutes of AF that are the products of diffusion through the amnion, and in the same token, less of it's own urine excreted at the opposite uterine pole will be swallowed, as more of it will be exchanged with maternal circulation before equilibrated with the AF of the cephalic pole. The IV hypertonic or the transamnionic isotonic glucose supplements, apart from improving fetal strength for swallowing, will also enhance the sweetness of the AF, making the fetal swallowing more voluntary. The normal new born behavior as observed by past researchers is a testament to all the above statements. The awake and a hungry newborn exhibits rapid searching movements responding to tactile stimuli, as far away as the sides of the jaw and the head (Brazelton 1986). The new born also has fine appreciation of taste, exhibiting preferential suckling response (with overall less pauses) when fed with different concentrations of sugar solutions, and great resistance to saline feeds (Johnson & Salisbury, 1975), more of such experiences increasing the complexity of the responses.
What Makes the Oxygen Diffusion Across the Cells of the Amnion, and the Interstitial Fluid that Permeates it's Canalicular System a Possibility—
From the intervillous space, to reach the fetal hemoglobin, oxygen has to traverse the following barriers before being bound to the fetal hemoglobin—
1. Maternal plasma, 2. Syncytiotrophoblast, 3. Cytotrophoblast, 4. A compact villous stroma made of fibroblasts, delicate collagen fibers, and Hofbauer cells, 5. Fetal capillary wall made of fully mature endothelial cells, and 6. Fetal plasma.
It means to say that before oxygen enters fetal hemoglobin, it traverses through maternal and fetal plasma interstitial fluid, and in addition, few cellular compartments. Similarly, oxygen can effectively traverse the membranous barrier of the amnion.
It is worthy of note that AF amino acid concentration is same as that of maternal plasma (R. Lisle Gadd), whereas glucose is present in lower concentration. The proteins are also lower. It is obvious that the amino acids have diffused into the AF from the uterine myometrium. Due to enormous growth and enlargement of the uterus to 10-20 times it's non-pregnant size, there has to be high amino acid turn over in the organ. Such high amino acid turn over, and the increased concentration as a result, are deemed to be reflected in the uterine interstitial fluid, and in turn in the AF (most probably by transit through intracellular and complex intercellular canalicular system of the amnion, as a cell pore size is much smaller than the molecular size of any amino acid). It is similar to the high trafficking of a raw material, needed for a local manufacture. The increased demand/metabolic rate/turn-over of a substance in conjunction with increased vascularity of an organ, can accelerate it's diffusion into the organ. Similar effect can be observed with respect to oxygen diffusion into the myometrium, also subject to similar setting, as oxygen is also a needed raw material for the profoundly increased mitochondrial citric acid cycle in each of the myometrial cells, saving ATP and glycogen. It was adequately stressed that cell/fluid bathers are deemed to be insignificant for oxygen diffusion and therefore it's simple diffusion should far surpass the amino acid transit via the amnion. The diffusion of O2 should be more efficient also for the reason that the oxygen having lower molecular weight than the amino acids, yet has to encompass smaller span of distance to exert it's desired effect over the fetus, and AF collection for measuring amino acid levels must have been randomly drawn, not necessarily from the AF adjacent to the uterine wall, and their levels are still equal to the maternal interstitial fluid.
The above matter of oxygen diffusion sufficiently into the AF is scientifically grounded, based on:
1. The standard laws of gaseous diffusion (as elaborately outlined earlier in this discussion favoring oxygen diffusion) across cell membranes and body cavities.
2. The presently available knowledge of the gaseous exchange at the lung and tissue capillary level based on the partial pressures of concerned gases, and their operative net diffusion gradient (the partial pressure and diffusion gradient of O2 during pregnancy deemed higher in non-placental myometrium/decidua).
3. The proved high CO2 content of AF by many past researchers (that was based on laws of gaseous diffusion and exchange of biological gases, as stated in 1 and 2 above).
4. The AF amino acid content approximating that of maternal extracellular fluid, so reflected due it's high turn-over in the adjacent uterine interstitium during pregnancy. Similar higher turn over in the myometrium is expected of oxygen also, with the laws of diffusion in fact favoring better oxygen diffusion than that of the amino acids.
5. The high PO2 of non-placental uterine interstitium further enhanced by the in-vicinity placental shunt effect.
It can be concluded that the maternal D-glucose supplements will increase the AF glucose content (also relieving the existing oligohydromnios, in a similar manner polyhydromnios is observed in maternal DM), and the improved volume as well as the palatability will heighten fetal swallowing of AF that contains more of glucose with sufficient amounts of oxygen also for it's aerobic oxidation (the intravenous hypertonic D-glucose therapy that is initially implemented can also supply needed ATP and the energy needed for swallowing, even in a previously moribund fetus). The isotonic D-glucose transamniotic supplements have similar direct effects.
It has been generally assumed that carbohydrate tolerance is impaired in pregnancy, and thus pregnancy constitutes a diabetogenic stress to the mother. The fact that diabetes is first manifest during pregnancy, and that the diabetic women frequently require increasing amounts of insulin as pregnancy advances, and the occurrence of glycosuria during pregnancy—are all cited as evidence to support this view. It is possible that it could be present earlier but uncovered during pregnancy, as it is a milestone event in time, and it is common rather than an exception that the mother as a whole is deservingly put under a microscope, making the statistical incidence of diabetes seem more than it's actual numbers.
However, interestingly, the normal fasting or post prandial/post glucose challenge blood sugar shows very close parallelism (in it's values and fluctuations) with the non-pregnant controls during pregnancy, in marked contrast to levels or patterns prevalent in diabetes itself.
Pregnancy is characterized by major physiological adjustments affecting every system of the body. The changes are frequently in a scale otherwise unseen in healthy non-pregnant controls, and can be legitimately subject to diagnostic concern and confusion. Such major change and a matter of great concern is the normally disproportionately elevated maternal serum insulin levels in the face of perfectly maintained blood glucose levels (in fact at a slightly lower level than the non-pregnant controls). Many other maternal serum values of clinical significance also show deviations that have to be interpreted with discretion.
There is reason for believing that many of the maternal changes are purposeful and mostly harmless, being directed to the welfare of the fetus. The fetal status in pregnancy is no doubt physiologically exalted, as obviously it is the only way that the theme of pregnancy can be accomplished. ‘The fetus thrives at the expense of the mother’ can be clinically evidenced by the fact that even when the mother is profoundly anemic due to iron deficiency, her fetus has grown well, and is rarely anemic. The author inventor had seen many such cases where the mothers' tongues were papery pale with their hearts pounding in hyperdynamic circulation, that gave room for concern how they ever survived pregnancy, but the delivered fetuses were pink to their extremities, as evidently the placenta concentrated iron very efficiently. It can seem as though the placenta worked solely and faithfully for the fetus, and conspired against the mother.
The insulin peak and the insulin antagonists—Blood insulin levels rise through pregnancy both in fasting state, and after glucose load. The insulin peak is especially dramatic late in pregnancy (from 125 μU of early pregnancy, it can rise in mid pregnancy to 175 μU, and it can be 340 μU in late pregnancy) (Spellacy W N et al, 1963 and 1965). This paradox of increased amount of circulating insulin while normal glucose levels are prevailing in the pregnant organism, is due to the presence of anti-insulin factors like glucocorticoids, estrogen, and the progesterone, but the most important insulin antagonist, as specified earlier, is the HPL, a polypeptide produced by the syncytiotrophoblast of the placenta. HPL produced by the placenta is only present in the maternal blood, but not in the fetus. Other possible culprits contemplated by past researchers are—(1) increased levels of xanthurenic acid—it is an accumulated tryptophan metabolite that can bind to insulin decreasing it's biologic activity, when the normal metabolic pathways of tryptophan are altered due to pyridoxine deficiency, usually prevalent in pregnancy (Zartman E R et al, and Spellacy W N. et al, 1972); (2) decreased chromium levels in pregnancy—chromium couples with insulin and may potentiate it's metabolic activity in the peripheral tissues (Davidson I W F, Burt R L, 1973); (3) Freinkel et al (1958) and Posner B I et al (1974) proposed that placenta destroys insulin with at least two soluble insulinase enzymes, and thereby there is need for more of it's production.
But the possible role of exponentially elevated maternal FFA levels, and the events encompassing it, and others, in causing maternal hyperinsulinemia, as contemplated in this writing by the author inventor, is discussed in the subsequent paragraphs.
HPL—HPL produced in enormous quantities in the placenta has great physiological significance during pregnancy. It causes increase of FFA content in the maternal circulation by mobilizing the lipid stores, and in this respect seems to be more dominant than insulin, because insulin is anti-lipolytic. Once there is increased FFA, the maternal tissues utilize more of it (in the adult human the FFA is the first fuel to be catabolically used) sparing glucose to be diverted to fetoplacental circulation which is a slower process, because the amount of glucose spared from all tissues of maternal body is much more and generalized, compared to the substantially lower amounts of glucose getting into the fetus only through the narrow channel of the umbilical cord (thus the maternal body intended to be acting as a glucose reservoir, for the sustained glucose supply to the fetus). As long as there is persistent normoglycemic levels of circulating glucose, it is expected to release insulin from maternal pancreas. However, the HPL, apart from mobilizing FFA from fat stores, also prevents insulin's effects on the cell membrane ‘carrier transporters’ of glucose in the maternal tissues, while the released free fatty acids further compete with glucose for their own utilization by the maternal tissues.
The maternal pancreatic response—The maternal pancreas is only conditioned to produce insulin as glycemic response, but does not perceive that insulin and also glucose are not being effectively used by the maternal tissues, except the placenta, and the fat depots. However, this fundamental homeostatic control though somewhat distorted during pregnancy is still not ineffective, because the rise of insulin proportional to glucose level (indeed a disproportionately high insulin rise) is needed to enable facilitated diffusion at the utero-placental interface, and to build maternal fat depots from early on, and is very relevant to enact the theme of pregnancy.
The lack of placental resistance to insulin even in diabetic pregnancy—As explained before, the placental tissues are deemed to be sensitive to insulin action even in diabetic pregnancy, as evidenced by fetal macrosomia, despite the maternal insulin resistance. Marshall R N et al and Posner B I et al in 1974 demonstrated that the placental binding protein of insulin is similar in molecular weight and in function to the insulin receptor protein found on the cell membrane of the maternal fat and the liver cells, that are also unaffected by the subject's insulin resistance, as obesity in diabetes is common rather than an exception.
(1) Insulin—Insulin normally is lipogenic. Hence, insulin rise is also important for the needed maternal fat deposition. It was previously mentioned that Vallence-Owen in 1965 had suggested that during insulin resistance as in diabetes, there is impaired uptake of glucose by the muscle, but not by the adipose tissues. It seems to be true also in pregnancy, as the essential fat deposition is not impaired, as would be expected of maternal insulin resistance. Such mechanism of fat deposition is obvious even in pre-diabetes, as in these patients, more the insulin resistance, more can be the manifest obesity.
(2) The biochemical factors—Biochemically, it is obvious that though hormone sensitive lipoprotein lipase (that is responsible for lipolysis) inhibition by insulin is impaired, the insulin's action on lipogenic enzymes like acetyl-CoA carboxylase, ATP-citrtae lyase, and fatty acid synthase has not seemed to be similarly undermined. This makes possible in the maternal tissues for both lipogenesis and lipolysis to be simultaneously ongoing, but at a different degree during different times. The maternal lipogenesis is dominant when the fetal FFA demands are less, almost showing a linear progression up to 25th week, when the curve gets plateaued until term. The mother seems to de-esterify these fat depot stores later on during pregnancy when the circulating FFA levels are found to be maximum during 37-40 weeks. It correlates with peak fetal lipogenesis, when the fetus can incorporate at this time the maternally derived FFA. In response to the same amount of hyperinsulinemia, the maternal lipid metabolic response during each trimester of pregnancy had proved to be different. In the second trimester as during the post-partum, the insulin's inhibitory effect on lipolysis seems to be 51% of non-pregnant controls, whereas in the third trimester it seems to be only 30% (Sivan et al, 1999) making maternal lipolysis maximally manifest during this period, for rapid fetal fat accretion incorporating the maternally derived FFA.
(3) Hormonal effects, increased food intake, and decreased physical activity—estrogen rise during pregnancy also seems to play a very important role in fat deposition, as it is very obvious that this sex hormone is what sets apart the sexual characters of the female body (apart from absence of androgens), and the same fat distribution can be evident in men castrated before puberty. It is obviously an evolutionary accomplishment of the races so as the females, needed for multiplication of the species, are not to be expendable biologically as a result of intermittent food shortage (NB. Myant). The presence of progesterone during pregnancy shall have added effect to lipogenesis acting at the hypothalamic level (F. E. Hytten). Improvising and additive to the increased food intake, the physical activity of the pregnant woman is lowered, with the metabolic rate set at a lower gear, mostly due to the thyroid hormone during pregnancy being bound, and inactivated. Both factors contribute to conservation of energy leading to maternal fat deposition starting very early on (F. E. Hytten).
1. The role of the circulating FFA of the maternal blood in causing maternal insulin resistance and hyperinsulinemia—
The maternal insulin peak seems to be the summative effect of anti-insulin factors (that are classically attributed to causing hyperinsulinemia), and also due to elevated FFA levels, as the insulin peak mirrors more of the heightened FFA levels late in pregnancy, than the steady state of blood glucose levels throughout. It is not to overlook the fact that insulin peak also correlates with glucose peak that is not as dramatic as FFA peak, and that without insulin resistance on glucose homeostasis, such insulin peak would have resulted maternal hypoglycemia.
In the second trimester as during the post-partum, the insulin's inhibitory effect on lipolysis seems to be 51% of non-pregnant controls, whereas in the third trimester it seems to be only 30% (Sivan et al, 1999) making maternal lipolysis maximally manifest during this period, for rapid fetal fat accretion. The lipolysis of third trimester is due to (many of) anti-insulin hormonal effects, that rise the FFA levels to the peak, which in turn can rise insulin levels, as insulin's inhibition on lipolysis is blunted, but not the stimulatory effect of FFA levels on insulin secretion (in a manner similar to glucose-insulin homeostasis, that insulin gets secreted as glycemic effect, while glucose itself is insensitive to it's effect).
2. The maternal fat deposition in causing maternal insulin resistance and hyperinsulinemia—
The maternal lipogenesis shows a linear progression from very early on, up to 25th week, when the curve gets plateaued until term. The fat deposition during pregnancy is mostly central, a state that resembles non-pregnant central (trunkal) obesity, and it can be speculated that the fat deposition (central obesity) acquired in pregnancy in such short term (due to many factors as seen in the preceding subsection of ‘stimulus for maternal fat deposition’) and at such rapid pace can also be accompanied by it's associated pervasive features of insulin-resistance and hyperinsulinemia, just as seen in non-pregnant obesity, mainly triggered by the obese-adipocyte, that is typically seen in central obesity. In non-pregnant central obesity, the molecular link between obesity and insulin resistance/effect seen in tissues such as liver, muscle, and in the fat tissue (Jeffrey S. Flier et al) can be explained as due to: FFA that are increased, and capable of impairing insulin action on glucose receptor sites; resultant hyperinsulinemia itself that can induce cell membrane insulin-receptor down-regulation; intracellular lipid accumulation in the adipoctyes, creating an ‘obese-adipocyte’, obesity generally being caused more by increasing in cell size rather than in the number of the adipocytes; various peptides including cytokines produced typically by obese-adipocytes are capable of modifying insulin action, an obese adipocyte being not only a lipid storage unit, but also an active endocrine cell that releases numerous agents in a regulated fashion. A factor called ‘resistin’ secreted by adipocytes can increase insulin resistance in this setting.
In essence, the exceedingly high circulating FFA, the rapid-onset maternal fat deposition, and the obese adipocyte, all associated with pregnancy can combindly exert powerful inhibitory effect on normal insulin action, and can explain the inordinately high insulin peak. Such mechanism of fat deposition and obesity being also obvious in pre-diabetes, and the fact that weight reduction even of modest nature can increase insulin sensitivity—are the testaments to what is likely induced by obesity and obese-adipocytes, as stated above. The recently evolved concept of metabolic syndrome, has central (abdominal) obesity, hyperlipidemia, and insulin resistance as three of the five features in it's constellation of associated metabolic disturbances.
3. Other maternal contributing factors—The essential amino acid arginine is an insulin secretagogue, whose action can be preserved even when glucose stimulated insulin secretion is impaired (Powers A C).
It can also be understood now that the maternal adjustments, as can be deduced from the scope of the discussion, are the result of an already over stretched adaptation even during normal pregnancy, being so many operational devices put together to divert the circulating glucose to the fetus, which can not be enabled any more during fetal IUGR of placental insufficiency. Maternal IV glucose supplement is similar to, but accomplished by easier means than what the maternal devices in pregnancy are trying hard to achieve. Glucose tolerance curves after IV glucose load show slightly lower values in all stages of healthy gestation, compared to the non-pregnant controls. Inferentially, there is evidence basis to believe that IV glucose supplements are well tolerated during pregnancy than in non-pregnant state which provides a sound basis for effectuating such clinical contemplation, however without overlooking the fact that insulin resistance is inherent to the pregnant state, and is inevitable.
How the Induced Therapeutic Maternal Hyperglycemia is Different from Diabetic State—
1. In the setting of fetal IUGR, following the therapeutically induced maternal hyperglycemia with IV D-glucose, the induced hyperglycemic peak is transient, and is of very short duration, with a maximum of an hour, mostly simulating an IV glucose challenge test, or the postprondial peak after a heavy meal, whereas in uncontrolled diabetes the hyperglycemic peak is persistent.
2. In diabetes, fetal hyperglycemia has resulted, whereas following the therapeutic maternal hyperglycemia induced in an IUGR pregnancy, the fetal hypoglycemia is corrected.
3. There is accompanying maternal ketosis in uncontrolled diabetes that is responsible for fetal anomalies, if such ketosis is significant during the first trimester, but ketosis is not part of the clinical picture in therapeutic maternal hyperglycemia.
Conventionally, the obstetric follow up of normal as well as at-risk pregnancy is monitored by bed side evaluation of the fetus/mother, and also by the diagnostic ultrasound evaluation. Before doing either, an accurate determination of gestational age is important on which the diagnosis of IUGR is contemplated and pursued. To accomplish that, complete and reliable history taking is paramount, and time spent on this is time worth spent.
History—As an IUGR fetus is initially suspected based on a reliable date of LMP (last menstrual period), a careful and detailed menstrual history is important. The combination of both reliable dates, but wrongly calculated gestational age happens in patients with oligomenorrhea with infrequent periods, for example every two months cycles. The obstetrician after noting a reliable calendar noted LMP, if forgets to note the patient's usual duration of cycles as two months, there will be a month incorrectly accounted for, in the calculated gestational age. If the patient's LMP was March 1, and if she comes on September 13, with no detailed menstrual history elicited, based on a calendar noted reliable LMP of March 1, her gestational age can be calculated as 28 weeks, when in fact her actual pregnancy duration is 23 weeks and 2 days. The pregnancy-wheel being based on the standard menstrual cycle of 28 days is the reason that the physician will come up with the gestational age of 28 weeks. In these patients, to calculate the correct gestational age, adjustment of days should be done based on ovulation timing, which is always 14 days before the first day of the next expected menstrual period (the missed period in the event of pregnancy), whatever be the length of the cycle. It is because the life of the corpus luteum is 14 days, unless the event of conception dictates otherwise, to prolong it's continued function of progestational support until the placenta completely takes over. It is a common understanding that ovulation occurs 14 days after the first day of a typical 28 day cycle. To be precise and all-inclusive—ovulation occurs 14 days before the first day of the next menstrual period, or 14 days before the date of the missed period (in the event of conception) of any type of cycle.
A simple and confident way to always calculate gestational age correctly—from a properly elicited menstrual history, note the date of the missed period (that is, if the cycle is of regular duration, though, the period is lengthened), and count back 28 days (exactly 4 weeks), and take that date as the LMP for calculation purposes (can be called CLMP, the corrected LMP, or LMP for calculations). From this date the corrected gestational age, and the corrected expected date of delivery (EDD) can be calculated from the wheel. In the exemplified patient with regular 2 months cycles and March 1, as LMP (the real LMP, and can be called RLMP), her date of missed period is May 1. Counting back 28 days, her CLMP is April 3, from which the EDD is calculated using pregnancy wheel. With this type of calculation the physician never has to worry or doubt his or her numbers in the rush of the out-patient clinic, emergency room, or after a night-call. The ‘Corrected Last Menstrual Period’ (CLMP) calculation can be stated as follows—‘With regular menstrual cycles but atypical cycle duration, count back 28 days from the date of the missed period to get the date of corrected LMP, for accurate calculation of the gestational age.’-Sumathi Paturu's rule for corrected LMP.
Or it can be simply said ‘Count back 28 days from the date of the missed period to get the corrected LMP’
The correct estimation of gestational age can be similarly done if the cycle is shortened, as a 21 day cycle, when the actual gestational age is 1 week more (if calculated correctly), which has practical implications in deciding interventions needed in a post-term pregnancy. If not correctly calculated, a decision can be made to deliver at 41 weeks or after, mistakenly calculated as 40 weeks or after. In this situation, if a patient's RLMP is July 1, and if she has regular 21 day cycles, her missed date is July 22, and counting back 28 days, the CLMP is June 24, from which the correct Expected Date of Confinement (EDC) or EDD is calculated.
A detailed menstrual history should include the duration of menstrual flow also, as after conception, some women can have spotting or 1-2 days bleeding that corresponds to the time of their cycles, which can be mistaken for regular periods by the patient, until such atypical bleeding ceases. In this instance the actual length of gestation is longer than what the patient reports as. U/S (ultrasound) confirmation is helpful, and it can be found to correlate with the typical LMP (as elicited by detailed menstrual history) being earlier than the reported LMP.
Different clinicians use different ways of calculating the correct gestational age when the cycle length is atypical, by adding or subtracting concerned number of days from the date of LMP or EDC. Some times, one may need a calendar to quickly and confidently correct the days, but the herein specified manner of calculating can be found useful, as it is quicker, can be done with out calendar, and not confusing. Above all, it is a better means to communicate in an objective and understandable terms, as there is a similar mode of calculation whether the cycle is shorter or longer than the typical 28 days menstrual cycle. Just as the configuration of the pregnancy-wheel used in the clinics, the Näegele's rule calculation also is presumptively based on the typical 28 day menstrual cycle, with the pregnancy duration of 10 lunar months (a lunar month comprises 28 days), that is 280 days, counted from the first day of LMP.
With the corrected LMP (CLMP) date configured in the manner as specified above, one can use the ‘pregnancy-wheel’ or the Nägele's rule to calculate the EDC from the corrected LMP. The Näegele's rule states—to get the EDC, add 7 days to the first day of LMP, and count back 3 months. It has to be noted that after adding 7 days, the month can change, and 3 months have to be counted back from that month. When mental calculation is done, it is easy to overlook such change in month. The Näegele's rule is very helpful when the pregnancy-wheel is not handy.
Clinical bed-side evaluation—a shrewd clinician can always diagnose IUGR by abdominal examination of the patient, in case the history is complete and reliable. To avoid observer bias, a single blind study can be used, in which unmarked paper strips can be used to mark the fundal height that can later be measured over a marked calipers. Or, the paper measure strip can also be used, one side unmarked for blinding. In obstetrics, a placebo effect on the fetal subject or the mother is not an expected clinical consequence.
When dates are uncertain, and as ultrasound estimation of fetal age by weight is discrepant in IUGR, standard ultrasound measurements may provide additional information about the true gestational age of the fetus for correctly planning for early delivery true to the gestational maturity. Due to the brain sparing effect of IUGR, the ratio of the head and the abdominal circumference (HC/AC) is in the 90th percentile in 60% of cases of fetal IUGR. Trans Cerebellar diameter (TCD) may be valuable (as the nomogram of Goldstein et al, 1987) in an IUGR pregnancy due to the ‘brain sparing’ effect despite growth restriction elsewhere, and it remains consistent through out, independent of fetal IUGR. The gestational age (in weeks) corresponds with the TCD in millimeters until 22 weeks, but the TCD accelerates after.
Ossification of distal femoral epiphysis occurs predictably around 32 weeks, and the proximal tibial epiphysis ossifies around 35 weeks. These two ossification centers can be noted as prominent echoes distinct from the rest of the bone image. Presence of distal femoral epiphysis of greater than 3 mm along with the presence of any proximal tibial epiphysis can indicate a mature lung in almost all IUGR fetuses (Galan H L, 2003).
Vascular Doppler Ultrasound evaluation—Doppler ‘Flow Velocimetry Waveforms’
(FVW)—the vascular Doppler study depends on the observations that: (1) the emitted ultrasound wave can be reflected, and the wave frequency can be changed, when a moving object within the circulatory system like the RBC is encountered by the sound wave; (2) the degree of change in the reflected and returning sound signal can be used to calculate the velocity/speed and the direction of the reflector (the RBC); (3) the over-all vascular doppler FVW form shows a clear systolic and also a clear diastolic component. All these principles are used to evaluate the resistance to blood flow in the uteroplacental circuit, and in turn the degree of placental insufficiency in an IUGR pregnancy. The effects of such placental resistance are also mirrored in the fetal vasculature, though manifest with different intensity in different vessels, also showing a different chronology as can be expected, based on the anatomical site of the vessel depicting the changes.
Doppler monitoring of Uteroplacental circulation—As pregnancy advances the uteroplacental blood flow gradually increases, mainly due to spiral arterial remodeling. Very early on, due to trophoblastic invasion, the endothelium and the smooth muscle layers of the spiral vessels are replaced, with loss of spiral artery vascular resistance. The lacunae further created in the syncytiotrophoblast by the cytotrophoblastic invasion and their filling with blood from maternal spiral arteries result in dilated blood pools of maternal sinusoids that are responsible for the shunt effect of the placenta. In pregnancies complicated by IUGR, the trophoblastic invasion is limited to the decidual endometrium with failure of the myometrial spiral arteries becoming low resistance vessels.
In normal pregnancy, the remodeling of spiral arteries dramatically decreases the peripheral resistance, an unique change that in turn can also be reflected in the Doppler Flow Velocimetry Waveforms (FVW) of the uterine arteries. It can be meaningfully discerned and interpreted, if the pre-pregnancy wave pattern of uterine artery or any artery in general is understood.
The normal non-pregnant (uterine) arterial pulse tracing: a normal arterial pulse tracing typically shows an upstroke followed by a down stroke. The UPSTROKE is abrupt without any secondary waves on it, and represents the initial part of ventricular systole. The DOWNSTROKE in the middle has a sharp depression called as dicrotic notch or the post-systolic notch, as this marks the early part of ventricular diastole. The dicrotic notch is due to sharp fall of pressure in the arterial tree caused by the rolling back of aortic blood towards the left ventricle at the beginning of ventricular diastole, when the ventricular pressure sharply falls. The rest of the down stroke of the pulse tracing represents ventricular diastole when normally there is no further filling of the systemic circulation until the next systole, when there is an abrupt systolic upstroke again.
The typical uterine arterial tracing changes in pregnancy are mostly due to the dilated placental sinusoidal shunt effect that continuously draws in the blood with no rolling back towards the left ventricle in this part of circulation, during the very early part of the ventricular diastole. There is also some continued filling of the placental sinusoidal spaces by the placental shunt-suction effect even through the late diastole, as if there is ‘spiral artery stealing’ of blood from the rest of the systemic circulation. These changes are shown in the uterine artery flow velocity wave forms (FVW) of a normal pregnancy, depicted as:
(1) loss of post-systolic notch (the dicrotic notch) in the middle of the down stroke of the tracing by about 26 weeks of gestation, and
(2) continued end diastolic flow filling shown as lifting of the down slope of the last part of diastolic tracing far up from the base line that continues until the next systolic upstroke.
However, these normal pregnancy changes are absent in the uterine artery wave forms of IUGR pregnancy that shows—persistence of post-systolic or early diastolic notch, and little end diastolic filling, or absence of increased end diastolic flow velocity. The terminal diastolic wave stays very near the base line due to little end diastolic filling.
Systolic/Diastolic ratio (S/D ratio)—it is defined as the ratio of the peak velocity of flow during systole and the peak velocity of flow during diastole. Progressive increase in placental vascular resistance with decrease in diastolic flow until the flow ceases, followed by reversal of the flow are ominous signs that need prompt further evaluation of the fetus. S/D ratio is the easiest to calculate, and is also the most commonly used. In the Doppler velocity waveform, if A represents the peak systolic flow velocity, and B represents the peak diastolic flow velocity, the systolic/diastolic flow ratio (S:D) is—
The Pulsatility Index (PI) of the flow—can be formulated as:
Uterine artery FVW analysis—it gained importance in screening for preeclampsia and IUGR at 20-24 weeks gestation. End diastolic flow velocities are not consistently present until after 15 weeks.
Doppler monitoring of Fetal circulation—From the fetal vessel Doppler Flow Velocimetry Waveform (FVW) it is possible to obtain the index of resistance in fetal circulation, that in turn is the result of resistance to circulation in the placental bed itself.
The Doppler Flow Velocimetry Waveforms are regularly used to assess resistance in fetal circulation, by monitoring more than one fetal blood vessel. It is based on the fact that there are sequential and definitive changes in doppler FVW resistance measurements in different vessels as the fetal IUGR is deteriorating, and that they are predictably typical in chronology.
1. Umbilical artery (UA)—60-70% of small placental arterial channels have to be compromised before the UA flow becomes abnormal. The S/D ratio is considered as abnormal if it is >95th percentile for gestational age, or if the diastolic flow is absent/reversed. Typically, the normal S/D ratio ranges as 1.5-2.5 in the third trimester. As the placental vascular resistance increases, the S/D ratio also increases. With the umbilical artery zero diastolic flow velocity, the perinatal mortality is 10%, and when the umbilical arterial flow is reversed, the perinatal mortality is 33% (Cunningham et al). Patients with oligohydromnios, and normal umbilical artery Doppler S/D ratio are less likely to have poor perinatal outcome. PI>2 SD (standard deviations) is considered as abnormal.
The development of terminal villi and their capillaries (whose contribution for the placental maternal-fetal exchange is significant) increases exponentially during 31-36 weeks of gestation, and it's failure could account for IUGR. It further contributes to the reduced umbilical artery end diastolic flow. Histometric support of this hypothesis is supported by observations of reduced terminal villi volumes as well as surface areas in IUGR pregnancies (Tesdale, 1984). Failure in the normal fall of maternal peripheral vascular resistance, usually by 16%, observed throughout normal pregnancy, can also be expected in this context.
The umbilical artery was the first fetal vessel to be studied in the normal and in the IUGR fetuses, and it was found out that the S/D ratio was elevated above 95th percentile in 85% cases of IUGR. The umbilical artery changes can be interpreted as due to: (1) the increased impedance in the umbilical artery blood flow as a direct effect of the resistance in placental blood flow, and as the fetal effects of ‘forcefulness of flow’(F), and ‘critical closing pressure’, the latter seen in small caliber vessels (‘law of Lawplace’) (see the discussion in a later section); (2) the changes in the viscosity of fetal blood, and sluggishness of the laminar flow, due to fetal polycythemia induced by fetal hypoxia; (3) the loss of the umbilical artery compliance, which in other words is the effect of critical closing pressure, as mentioned. It is worthwhile noting that the umbilical artery has helically arranged muscles wherein 50% contraction causes complete occlusion, whereas 50% contraction of a simple circular muscle merely reduces it's lumen caliber (Von Heyek, 1935).
2. Middle cerebral artery (MCA)—it was adequately stressed earlier that in the setting of uteroplacental insufficiency, the fetus adapts by directing more blood flow to vital organs like brain, heart and the adrenal glands by vascular auto-regulation. The fetal brain normally has a high resistance flow pattern compared to other large vessels. However, the Doppler FVW form study of the IUGR fetus depicts in the middle cerebral arteries an increase in end-diastolic blood flow velocity that in turn is reflected as low Doppler index of flow resistance. The MCA being positioned perpendicular to the mid-line of the brain, the Doppler beam can be easily positioned along the mid-point of the vessel, with a minimal angle.
Capponi and associates also showed that the MCA pulsatility index (PI) is decreased in IUGR, and it is the best predictor of fetal hypoxia.
The reduction in the fetal abdominal circumference (AC) precedes the Doppler abnormalities of both fetal umbilical artery and of the MCA. The decrease in the vascular resistance of MCA, and the increased vascular resistance of the umbilical artery, both were found to begin more than 3 weeks earlier than the non-reassuring fetal heart rate recordings (Galan et al). The above fetal brain-sparing by cerebral auto-adaptation to hypoxia is a sign of appropriate fetal response, and loss or reversal of such brain-sparing effect is considered as a late or ominous sign in a decompensating fetus, and a warning for urgent obstetric interference. With reversal of brain sparing auto-regulatory adaptation, fetal mortality approaches 50%. Loss of brain-sparing effect in the MCA can be confirmed by checking Doppler FVWs elsewhere, especially on the venous (precordial) side, which waveforms will be found abnormal as well.
The ratio of MCA pulsality index (MCAPI) and the UA pulsality index (UAPI), that is, the ratio MCAPI:UAPI was found to be more valuable in recent studies, by Shahinaj et al from Tirana, Albanie. It incorporates data that indicates not only placental state (in UA), but also the consequent fetal response (in MCA), which is advantageous in predicting perinatal outcome.
As was noted earlier, in normal pregnancy the cerebral arteries show high resistance flow pattern at any time during gestation, with resistance higher than placental resistance, and a resulting MCAPI:UAPI ratio of 1.08. The results of taking the above ratio into consideration (with ratio of 1.08 as normal, and <1.08 as abnormal) added positively to predicting the outcome.
The following are the reference abnormal values pertaining to the vascular Doppler velocimetry—
The observations and deductions of the above researchers pertaining to MCAPI:UAPI needs further comment. It has to be noted that the fall of MCA resistance indicates a compensated fetus. After documentation of such observation, if fetal compensation fails, the MCA Doppler flow resistance will rise again, which is worse. Hence when interpreting the MCA Doppler FWV form with reference values as above, a longitudinal study with sequential changes in the values are meaningful (as the interpretation can be discrete in reflecting the values true to the fetal state), rather than a random cross sectional value in isolation that may not bear correlation to possibly deteriorating clinical events, unless UAPI also rises by that time, making the ratio <1.08.3.
Venous and cardiac flows—the Doppler velocimetry has been used to study the venous circulation of the IUGR fetuses, like the circulation in the umbilical vein, the hepatic veins, the ductus venous, and the inferior vena cava (IVC). Interesting correlation was found between the abnormal changes in these vessels, and the fetal acid-base changes.
(a) Ductus venosus—A decrease in the velocity of a-wave is the characteristic abnormality in the ductus venosus. In the normal venous flow pattern, the a-wave form is characterized as below.
Baschat and colleagues (2007) in their study involving 604 neonates delivered less than 33 weeks gestational age whose ultrasound abdominal circumference (AC) was less than 5th percentile, concluded that changes in the ductus venosus doppler velocitometry is primary in predicting neonatal outcome. The changes were due to fetal myocardial deterioration and acidemia. If the ductus venosus shows reversal of blood flow at 26-28 weeks, it is a late sign, as the fetus has already sustained irreversible multi-organ damage. It implies that one may not wait for these changes to decide for delivery.
(b) Umbilical vein—normally the umbilical vein blood flow is monotonous, and the presence of pulsations or nicking corresponding with FHR is secondory to ventricular failure. It is a late sign of a decompensating fetus. Changes caused by fetal breathing can mimic nicking or pulsations of umbilical vein, and can be differentiated by looking for their coincidence with fetal breathing motions. The rate of the umbilical vein pulsations seen in the umbilical vein Doppler waveform should be recorded when possible, when fetal breathing movements are of concern as in an unequivocal BPPS (biophysical profile scoring).
There are three identified umbilical venous patterns—(1) a monotonous umbilical vein flow pattern in a resting fetus (as normally the positions of great veins are not retrogradely transmitted into distal veins, unless the great veins are enormously engorged); (2) an undulating umbilical vein flow pattern corresponding to fetal inspirations (transmitted from closely approximated liver and diaphragm) that are lower in frequency, and further confirmed by coincidence with fetal diaphragmatic movements; (3) the umbilical vein wave flow pattern corresponding in rate with that of the fetal heart rate itself as specified above—the waves originate in the right atrium, and propagate in a retrograde manner into the venous tree, and in proper context represent late stage of fetal heart failure, with associated fetal hypoxia and acidosis.
The Sequence (Chronology) of Fetal Monitoring for Predicting the Fetal Well being/Time of Delivery in IUGR—
In monitoring an IUGR fetus, a study of Doppler changes cross-sectional in time is important, but the chronology of the longitudinal changes (the serial changes in time) and it's reliable correlation with fetal deterioration are even more important to assess the risk of prematurity vs. sudden fetal demise, and to deliver the severely distressed fetuses just in time. In 2001 and 2002, three Doppler FVW studies clarified that a deteriorating fetus does show particular sequence of doppler changes prior to significantly abnormal non-stress test (NST), and an abnormal biophysical profile (BPP) that would normally warrant immediate delivery. The well biophysical profile (BPP) that would normally warrant immediate delivery. The well differentiated chronology of Doppler changes is categorized as early and late changes as follows—
1. Early Doppler changes—
The biophysical profile uses 5 components to be evaluated during a stretch of 30 minutes duration. Each component is scored either as 0 or as 2, with a total best composite score as 10, and the worst as 0. The scoring criteria are tabulated in table-6.
The standard BPP score (BPPS) interpretation, and the normally pursued action plan—Score 8-10—normal; score 6—equivocal or suspicious, repeat test the next day; score 4—repeat test in 12 hours, and if score is ≦6, plan immediate obstetric interference.
Among the 12, 620 women tested weekly with BPP, Manning and co-workers reported the following statistical significance of the test: false negative rate-0.06%; false positive rate-40% with BPPS of 6, and 0% with BPPS of 0.
The fetal umbilical vein (containing oxygenated blood) blood pH shows the following correlation with the BPP score (Manning et al): BPPS 8-10-pH 7.37 (in the normal range); BPPS 6-pH 7.33; BPPS 4-pH 7.28; BPPS 2-pH 7.2; BPPS 0-pH 7.08.
Basis for the test—if the fetus is neither acidotic nor hypoxic, the fetal heart rate accelerates with the fetal movement.
In association with or following fetal movements, the fetal heart rate shows transient heart rate accelerations, and there should be at least 2 such transient fetal heart rate accelerations within 20 minute period after the test is started. Each heart rate acceleration should normally last at least 15 seconds, with the peaking of the fetal heart rate by at least 15 beats per minute above the base line. Conventionally, it is done once a week, but doing twice a week reduced fetal demise by threefold. It implies with certainty, but not always, that the fetus will survive in-utero until the next test, that is until one week. But in high risk pregnancy remote from term, the test can be repeated even daily, or twice daily. However, the NST observations must be interpreted as per the gestational age, because fetuses less than 34 weeks do not always respond by ‘accelerations of 15 beats lasting 15 seconds’ criterion. It is prudent to allow 40 minute or longer wait period for fetal sleep cycle, to conclude as an insufficient fetal reactivity. A time saving, and more reliable way of doing BPP/NST is the below described acoustic stimulation test (AST).
The acoustic stimulation test (AST)—some times the fetal sleep cycles can be longer, and to eliminate the possibility of a false nonreactive test, loud external sounds have to be used to startle and wake up the sleeping fetus. A commercially available acoustic stimulator can be used to elicit acoustic stimulus on the maternal abdomen, repeated upto 3 times, for upto 3 seconds (ACOG 2007). With the use of the AST, the standard time duration mentioned in the above table can be observed for all the relevant tests, without a wait period of 40 minutes or more.
False negative tests are exceptionally low with NST. Large clinical trials inferred false negative results to be less than 0.7%. NST also more frequently identified a fetus in jeopardy than the Doppler FVW pattern had identified.
The Fetoplacental Pathogenesis as Depicted in the Doppler FVW Form and in BPP Score Abnormalities, and their Possible Remedial Measures—
Fetoplacental pathogenesis as depicted in Doppler ultrasound—Undoubtedly, the fetal vascular Doppler abnormalities had originated from placental resistance, but there is also no doubt that subsequent fetal contribution significantly worsens the picture, making it a vicious cycle. The vascular resistance that manifests in the umbilical artery has two components—placental and fetal. The placental component needs no further explanation. The fetal component is multi factorial, but the root cause is hypoglycemia with no energy reserve or lack of ATP for efficient contraction/tone anywhere in the fetal musculature (poor tone, reflected in BPP) including the myocardium, that results in poor cardiac contractility, suboptimal stroke volume, and low cardiac out-put. To start with, the systolic output needs to be sufficient, so that there is enough reserve volume in the systemic tree during diastole, after the blood runs off into the smaller vessels and veins.
The flow through a vessel is dependent on two factors—(1) the pressure difference between the two ends of a blood vessel concerned, that is, the umbilical artery in this setting, and (2) the impedance to flow, that is, the vascular resistance within the vessel, expressed as:
wherein, F represents the rate or forcefulness of flow through a vessel, P1 the pressure at the origin of the vessel, and P2 the pressure at the other end of the vessel, and R, the impedance to flow. It has to be noted that it is the difference in the pressure between the two ends of the vessel, and not the absolute pressure within the vessel that determines the rate or forcefulness of the flow (Guyton A C). To exemplify the statement—if the blood pressure at both the ends of a vessel is 60 mm/Hg, the flow ceases, though there is high absolute pressure of 60 mm/Hg within the vessel. If the blood pressure is 80 mm/Hg proximally, and 60 mm/Hg distally, blood flow distally is possible. It can be noted that an optimal pressure at the proximal aorta can be only achieved by effective stroke volume that lasts in the arterial tree through the cardiac diastole also (i.e. what has remained after the blood runs-off into the capillaries and the veins during systole). No doubt there is high pressure distally in the fetal umbilical artery due to placental resistance, but there is low pressure proximally at the fetal descending aorta level also, due to inefficient fetal cardiac contractility. This in turn can be due to many factors that can build up as a vicious cycle. ATP needed for effective cardiac contraction can not be generated for various reasons like—(1) fetal hypoglycemia, (2) failure of pyruvic acid to enter or continue in citric acid cycle due to fetal vitamin/mineral deficiency, or else (3) fetal hypoxia. To compensate hypoxia, the fetus responds by tachycardia to draw more of oxygen from the placental bed. But tachycardia can only happen at the expense of diastolic time (systolic time is constant what ever be the heart rate), drawn from each cardiac cycle, and in turn at the expense of coronary filling, because coronaries fill only during diastole. That means, the fetal heart is working more, but any more than optimal average rate of 140 per minute can lead to coronary ischemia in a hypoxic fetus, and what seems as compensatory tachycardia does not serve the purpose of increased myocardial oxygenation, but will certainly cause increase in long-term cardiac work load, leading first to compensated cardiac failure, and later, decompensated failure manifesting as bradycardia. As the great veins and the venous tree comprise high compliance and high capacitance vessels, the venous side accommodates many times more blood than the arterial side, during the process of compensated or decompensated cardiac failure that further reduces the blood getting into the heart. This in turn leads to progressive diminishing of cardiac stroke volume during systole. Essentially, the fetus is in hypotensive state that is responsible for ineffective maintenance of diastolic blood pressure that is shown as decreased diastolic flow velocity of the doppler waveforms, or even as reversal of flow. Thus the fetal hypoglycemia and hypoxia with ineffective cardiac contraction, and low P1-P2 can be directly proportional to the diminished forcefulness of the flow, which is added to the inversely proportional high peripheral resistance R, contributed by the placental resistance. Fetal polycythemia and the increased blood viscosity also contribute to decreased flow velocity, and the high fetal sympathetic tone due to continued intrauterine stress can additionally contribute to persistent fetal tachycardia. With fetal heart rate as 140 per minute, each cardiac cycle lasts 0.428 seconds. If fetal HR goes up to 160 per minute, the cardiac cycle lasts only for 0.375 seconds. The decreased time of 0.053 seconds which is 12.38% decrease of the normally allowed time for each cardiac cycle (with the optimal 140 beats per minute) is happening by consistent cut off from the ‘diastolic coronary filling time’. That is, for the fetus, it is 2 hours and 58 minutes per day loss in the coronary filling time. It is imposed on the top of the long-term strain of increased cardiac work load of 20 extra beats per minute. Restoration of fetal heart rate to optimal number early on can prevent fetal myocardial work load.
It is worthy of note that the umbilical arteries being the branches of fetal internal iliac arteries, are not high caliber vessels to start with, and in turn they are subjected to the physical laws of ‘critical closing pressure’ seen in small caliber vessels, as is dictated by the law of Laplace. Though each umbilical artery receives 20.5% of the fetal total cardiac out-put (Rudolph and Heyman, 1968), the absolute flow through these vessels is very less, that is only 100 ml per minute/kg at 22 weeks, and 300 ml per minute/kg at 37-38 weeks (Gill and co-workers, 1981). The above are even lower volumes, if calculated per fetal cardiac cycle, flowing into the placental circuit. One may consider that they are proportional to the fetal size, but the dynamics and the physical laws of blood flow are neither different nor forgiving, because they are directed to the fetal vessels. In an adult, at 20 mm/Hg blood pressure, blood flow in the smaller vessels entirely ceases, that being the ‘critical closing pressure’ (Guyton A C). The vasomotor tone of the smaller arteries is always attempting to constrict these vessels to smaller diameters, whereas the blood pressure inside is attempting to dilate them. When the pressure in a vessel falls, also decreasing the vascular diameter, the muscular forces tending to keep the vessel wall stretched, decrease extremely rapidly (Guyton A C).
The law of Laplace states—the circumferential force (F) tending to stretch the muscle fibers of a vessel wall is proportional to the diameter (D) of the vessel times the pressure (P) with in the vessel. It can be shown as: F∝D×P.
The law explains that more the blood pressure falls decreasing the effective diameter of a vessel, further more the vessel wall will close, which also is a vicious cycle. To make the situation worse, the umbilical artery has helically arranged muscles wherein 50% contraction causes complete occlusion, whereas 50% contraction of a simple circular muscle merely reduces it's lumen caliber (Van Heyek, 1935). Hence, it is imperative that adequate fetal cardiac contractility, optimal stroke volume, and normal range diastolic blood pressure are maintained in fetal arterial tree, and in turn in the small caliber umbilical arteries.
BPP—Impaired energy reserve/ATP is responsible for lowered over-all fetal movements, and the lowered muscle tone (just as the lowered fetal cardiac muscle contractility described above) that are reflected in the lowered score of BPP. Essentially, the low BPPS represents a fetus of low energy, i.e overall fetal apathy.
Maternal rest in left lateral Trendelenburg's position—It may be noted that in a cephalic presentation with the placenta located in the upper uterine segment, when the mother is in standing or sitting posture, the blood in the aorta and the hypogastric vessels (that form umbilical arteries) of the fetus have their blood flow towards placenta, flowing against gravity. Gravity may also make the loops of umbilical cord to settle in the lower uterine segment (unless interrupted by fetal body parts) from where the blood has to flow upwards towards the placenta, also against gravity. Hence this writing advocates maternal bed rest in left lateral Trendelenburg's position (head end inclined lower than the foot end, best achieved by raising the foot end of the bed by solid blocks) that can have impact in overcoming the forces of gravity, and the placental resistance. Though the fetal position is unstable earlier in pregnancy, yet in this position the placenta and the umbilical cord will be still situated at a lower level than the fetal heart. The uterine artery course that becomes descending instead of ascending can compensate maternal abdominal aortic flow that becomes ascending. This maternal positioning also takes into consideration of the facts that the maternal cardiac function is appropriately hyperdynamic to pump efficiently into the ascending thoraco-abdominal aortic column, and the uterine circulation that is locally sub-optimal for whatever pathology is deservingly benefited by the descending column of blood within the uterine artery. With the loops of the umbilical cord also displaced nearer to the placental plane of the upper uterine segment, the blood flow is not against gravity which can improve the flow impedance in the umbilical artery. While the foot end of the bed is raised by blocks, the mother should have one or two pillows under her head and neck, to avoid pressure effects in the head in due course, like facial puffiness, nasal congestion etc, symptoms that manifest even during normal pregnancy. Trendelenburg's position though theoretically appealing, can be impractical. Hence, at least bed rest in general can have tremendous benefit, if advocated with correction of other major deficits.
It is also helpful to inquire if the mother has gastroesophageal reflex disease (GERD) to be treated with medications for GERD, and to be advised to sleep as advocated above.
The term lower uterine segment though generally used in obstetrics during labor, in this writing, it is used throughout to denote the lower anatomical part of the uterus, and must be so understood.
Correction of unobvious maternal factors, though considered as insignificant, they can still help, in case they are few of the many culprits operating in unison. It is the tight fitting maternal clothing, especially the pre-pregnant bra that she had long ago outgrown during pregnancy. Full chest expansion, especially to allow for the needed pregnancy adaptation of respiration, is very important, and the front wire-rimmed bras have to be especially discouraged, as they restrict the full expansion of the anterior hemithorax with decremented tidal volume, defeating the fine tuning of the nature's concert of pregnancy orchestration. The progesterone-driven pregnancy hyperventilation has a purpose. The pregnancy minute volume increases by 40% almost entirely by increase in tidal volume rather than respiratory rate, that causes decrease in expiratory reserve volume, with alveolar ventilation increasing by 65%, and PCO2 decreasing significantly for the needed gradient at the placental level (Hytten F. E). Low oxygen concentration in any area of the lung due to hypoventilation causes pulmonary vasoconstriction in that area, an adaptation to direct the blood flow to better aerated lung fields, a feature unique to pulmonary circulation. If the hypoventilation (with reduced PO2 of alveolar air) is generalized due to mechanically restricted chest expansion, generalized pulmonary vasoconstriction can ensue, with resultant lowered PO2 of maternal arterial blood, that will be added to the higher value of PCO2, both values not adapted to pregnancy range. If there is shortness of breath due to ill-fitting clothing, the mother may attribute it as the natural consequence of pregnancy itself.
The mother should be further advised to wear increasing sizes of bras as the pregnancy advances. The best way to demonstrate that she is wearing a tight fitting bra is to let the nurse unhook the bra, and observe how much apart the bra ends will recede from each other during full inspiration, and to let the mother be surprised to feel that gap with her hand, and know the measure of chest circumference she is not allowing to expand. The nurse should be trained to observe/document the concerned observations. The chest expansion/measurement can be more while sitting than standing. The best option of the mother is to try the bra size while sitting, and buy one size larger.
Tight fitting jeans (or outgrown dress pants, or tight dress skirts) should also be curtailed, as they can press the gravid uterus against the great vessels. Such tight garments can have an effect worse than supine hypotensive syndrome, as the pressure on the uterus can be all through the wakeful hours. The patient may be considering to replace her regular garments only when it becomes impossible to wear, without knowing the adverse effects on her pregnancy, and with compensated asthma, COPD, heart diseases, smoking etc. the effect on pregnancy can be significant. In fact, these subtle factors can be operating in IUGR with no known etiology.
(1) By maternal hypertonic D-glucose supplements, an adequate supply of D-glucose to both the fetus and the placenta is ensured. It is to be noted that placenta consumes 50-60% of glucose getting into the placental interface, and 80% of it is converted into lactate that is supplied to the fetus during times of need. Fetal heart (and also the fetal brain and skeletal muscle) efficiently metabolizes lactate just as it metabolizes glucose (see also the section ‘The improvement of fetal lactic acidosis/pyruvic acidosis). Maternal IV glucose supplements during midnight, or IUGR-diet snacks in between meals can be valuable in this regard to ensure almost continuous fetal D-glucose supply, or else to improve placental lactate reserves, stored with no O2 expended by the placenta.
(2) Cessation of fatty acid oxidation saves 33% of oxygen, improving myocardial oxygenation, fetal tachycardia, coronary filling, and fetal cardiac function needed for optimal stroke volume.
(3) With glucose availability, fetal body protein break down for dire energy needs is curtailed, the amino acid source of energy being worse than the lipid source in it's ATP/O2 expenditure.
(4) Fetal energy for swallowing of the AF improves.
(5) Placental active transport of many elements, mostly of minerals and vitamins that the placenta concentrates, is dependent on placental availability of glucose to generate ATP continuously, needed for such active transport. Iron, calcium, magnesium, and B-complex factors are all vital and scant in the maternal compartment and the active transport is the only means of their fetal acquisition. Though the compensatory polycythemia in IUGR is mainly a reflex fetal response to hypoxia, it is essential that the fetal RBC has the needed optimal MCHC with the improved iron moiety of hemoglobin also contributing for the relief of fetal polycythemia that in turn relieves the sluggish laminar flow in all vessels. The implemented oxygen therapy in the treatment protocol will further benefit persistent fetal hypoxia, and it's accompanying adverse fetal effects.
(6) The IUGR diet with rich supply of essential amino acids of which arginine is a part, will contribute to the compensatory synthesis of nitric oxide (the body's integral element needed for vasodilation throughout) in the terminal villus vasculature as well as in the umbilical vessels improving the umbilical artery compliance, end diastolic flow velocity/volume, and hypoxia.
The hyprtonic D-glucose and IUGR diet exert their invaluable effect, first of all by breaking the vicious cycle of established adverse path ways, after which the fetal milieu can be better amenable to any positive physiochemical benefits of such therapeutic maneuvers. Hence their therapeutic trial is warranted (especially when a fetus is not viable for delivery) either the fetus is in compensated, or decompensated (cardiac) failure, and what ever be the nature of Doppler FVW form at the outset. Doing something is better than doing nothing, at least for one reason to start with—for the relief of distress both to the mother and to her clinician that is invariable in inaction, whereas at a later date, the unrelievable fetal distress may be found to be surprisingly relieved.
The novel invention sets forth desirable attributes for successful treatment of a so far truly evasive disease entity in the specified art of obstetrics, encompassing a treatment that is: safe, simple, minimally invasive, risk free in terms of fetomaternal mortality/morbidity, non-anxiety provoking, and most important of all, one that was proved successful, as evidenced by a successful case study of severe fetal IUGR, treated by the author inventor. Being simple, it's method is easily reproducible over desirable long term with similar anticipation of success. Most importantly, the treatment is based on sound and infallible scientific model conforming to the needed ‘as a whole inquiry’ approached and clarified with biochemical/physiological rationale befitting every new encounter, as seen in the preceding sections.
In alleviating the placental insufficiency of fetal IUGR, an accelerated ‘Facilitate diffusion’ of glucose can be achieved in the afflicted placenta, by creating transient hyperglycemia in the mother by hypertonic glucose 25-50%, up to 50-100 cc twice or thrice a day, given as a bolus intravenous injection over a period of 3-5 minutes, such treatment initiated as soon as it is confirmed that the fetal IUGR is of vascular in origin. When the therapeutic trials of maternal IV treatments are exhausted without substantial benefit, as later discussed in detail, transamniotic isotonic D-glucose supplements are initiated, the amniotic cavity accessed through a subcutaneously implanted pregnancy-port (SIPP) catheter via an extraperitoneal suprapubic approach, with novel structural and operational modalities that are easy to implement.
Apart from the classic preeclampsia/eclampsia, the varied pathological states subject to fetal growth restriction of vascular origin, and can be similarly benefited are: chromosomal anomalies found to be associated with reduced number of small muscular arteries in the tertiary stem villi, chronic placental separation, extensive localized placental infarction, circumvallate placenta, velamentous insertion of the cord, one or both the twins affected due to reduced trophoblastic area available to each, to mention a few (this list is not construed to be exhaustive). They are unseemingly though clinically responsible for the diminutive placental exchange, and for the fetal IUGR. Clinical diagnosis of a vascular pathology is not feasible in all circumstances, and hence as a diagnosis of exclusion, any suspected fetal IUGR can be offered a therapeutic trial.
Accounting legal implications—The treatment of fetal IUGR with maternal hypertonic glucose supplements is not without legal implications, if not done discretely. This is due to the unavoidable interference with the maternal carbohydrate metabolism. The natural course of diabetes in a patient ultimately destined for it, during pregnancy or after, becomes imperceptible from what is benignly interfered with pertaining to carbohydrate metabolism, through the treatment itself (refer 1(b) of the section ‘The author's theory to account for the manifest maternal hyperinsulinemia during normal pregnancy’ to understand the natural history of gestational diabetes). For that reason, adequate patient education and a strong therapeutic alliance with the patient are paramount. This needs the patient's equal participation in all decisions for her treatment. A strong basic knowledge is important to clarify patient's questions/concerns, and for confident clinical management also required in invoking patient's confidence, as for either, there is no short cut.
Careful history taking with regard to family history of diabetes, and for clues of previous gestational diabetes is important. IUGR in a diabetic pregnancy is rare, but possible, when hyperglycemia is marginal, and such rare encounters that can put the obstetrician in a dilemma, need in depth discussion. Whereas the hyperglycemia can be just few numbers above cut off values, the induced hyperglycemia is more pronounced by it's higher blood sugar range, and hence significant in overcoming the placental impedance. In this situation, making decision about maternal versus fetal well-being can be daunting, and needs significant understanding on the patient's part. It has to be honestly informed to the patient that postponing the treatment of her diabetes by few months will not significantly affect the natural course of the disease, as the disease consequences slowly evolve over very long term, and after delivery, every stringent measure followed through years will equally contribute to the best ultimate outcome. This is also assured by the specialist (who should be called throughout, as ‘diabetes specialist’ instead of an endocrinologist) for the needed patient trust, apart from relieving her anxiety and possible indecision. Careful monitoring to prevent adverse events of diabetes is necessary, and information pertaining must be given to the patient as written instructions, apart from her signed alliance to cooperate with/follow needed frequent monitoring. Above all, decision for treatment should be entirely made by the patient, along with her signing a therapeutic alliance for no physician responsibility for what ever be the course of diabetes (if worsened soon after pregnancy, or years later), or the outcome of the baby. Indeed, the course can be unpredictable for number of reasons, and one can be the patient's non-compliance itself later on, in the treatment of her mild diabetes. The patent's chart should be preserved even after the obstetric relationship is over, as any patient, if needed to be treated with insulin for uncontrolled diabetes later on in life can be aggrieved for such need and out-come, and can pursue legal course, forgetting all ‘therapeutic-agreements’ she made years ago. Demonstration of fetal growth soon after treatment will be a gratifying incentive both to the patient and to her obstetrician to follow the same, until the fetal viability is assured for an earliest possible delivery. These patients should be watched for hyperosmolar syndrome, ketoacidosis etc. just like any other diabetic patient, and treated similarly. Hyperglycemia is targeted only to the extent that the desired fetal growth is achieved, and no more. Fetal anomalies due to uncontrolled diabetes are as a result of uncontrolled ketonemia in the first trimester, and such danger is never a clinical consequence during the second trimester and later, when the patient is being treated.
A sincerely vigilant attitude, both clinically and personally towards the patient from early on is important to gain her trust, which also enables the patient to ungrudgingly and understandingly accept any adverse outcome, and realize that her physician had done the best that can be possibly done, in her situation. A written summary of: the natural course of diabetes, the unique effect pregnancy itself has on blood sugar control, the contemplated modality of treatment, and the imperceptibility of the effects of treatment from the natural course of diabetes for those destined for it—should be given as a hand-out to all, on the first encounter. The obstetrician should take time to answer all the patient's concerns and questions, and then proceed with clinical decision making carefully but swiftly, as there is no time to waste, as each day passed has it's toll on the fetus, and the ultimate pregnancy outcome, a matter that needs to be conveyed to the patient also.
In the majority, as the onset of fetal IUGR falls around the time that the mother is screened for diabetes at 28 weeks, the obstetrician is already aware of the patient's glucose tolerance, and if not, it can be immediately ascertained. The screening is done with 50 g oral glucose, without regard to prandial state, or time of the day. To test, a single venous sample is drawn at 1 hour.
The normal blood glucose level cut-off at—130 mg/dL—has 90% sensitivity, and
The American Diabetic Association (ADA) and the ACOG agree with either of the threshold values. For all positive tests, WHO and ADA recommend a 3 hour OGTT (oral glucose tolerance test) with 75 g of glucose and the diagnosis of diabetes mellitus is made when two or more venous plasma glucose values are at or above the following standardized values, approved by the ADA—
1. Thiamine—all patients should be given 100 mg of IV/IM thiamine (B1 vitamin) before IV hypertonic D-glucose treatment. This is done even with prior oral supplements in a compliant patient. The obstetrician should document such therapy in terms of point in time, that is, prior to IV glucose treatment. It is for the reason that after glucose load, thiamine deficiency can precipitate pyruvic acidosis/lactic acidosis in a previously malnourished patient. Malnutrition is not uncommon in this subset of population due to alcoholism, hyperemesis, and pregnancy pica in the socioeconomically well-to-do cultures, but under-nutrition can be a contributing factor in the developing countries.
2. Multivitamins/minerals—all patients should have IV multivitamins/minerals supplements that includes generous amounts of phosphorous (assuming patient's renal function is optimal).
3. Magnesium—magnesium supplements is considered separately due to it's specific deficit in malnourished patients, and due to the vital role of magnesium in all biologic functions where ATP is involved, which is ubiquitous, as it is Mg-ATP that actually participates in such reactions.
4. Potassium levels are needed to be monitored initially during IV hypertonic glucose treatment to note occasional undue fluctuations.
IV hypertonic D-glucose treatment, and the blood glucose parameters—The amount of IV hypertonic 25-50% glucose supplements given to the patient (mother) as 50-100 cc bolus twice or thrice daily should be individualized. As evidenced by the treatment done by the author, such maternal therapy is deemed very safe, and well tolerated in individuals with no inherent predisposition to impaired glucose tolerance. However, it is a good idea to start with smaller dose such as 50 cc of 25% glucose, and to progressively but swiftly increase to 100 cc of 50% glucose. Such progressive therapeutic augmentation is done in the hospital, as the devised protocol, with also monitoring of blood glucose values, and of the potassium response initially.
With 25 G of glucose (equal to 25% glucose as 100 cc, or 50% glucose as 50 cc of therapeutic hypertonic glucose supplements), injected as IV bolus over a 3-5 minute period, the following blood glucose levels can be expected—a peak of 175 mg % at 15 minutes, 125 mg % at 30 minutes, and back to normal non-pregnant level of 75 mg % at 1 hour, and further declining to slightly lower levels of 70 mg % during the second hour. These levels were the average results of 120 pregnant women tested during pregnancy by Spellacy W N et al in 1964-65.
The above numbers also demonstrate that in a healthy pregnancy (with respect to glucose metabolism, and not IUGR) the normal glucose levels are attained in the maternal circulation within one hour. In the same token, advocating the therapy in between meals and at mid-night, and additional frequent intake of IUGR-diet snacks will create more of such hyperglycemic peaks in the mother, without inducing adverse effects on the carbohydrate metabolism. In fact, the IV hypertonic glucose supplements mimic post-prandial glucose peak, and can be compared to a situation where a mother has a tremendous appetite and is eating three meals and also equal sized snacks in between. That type of food intake is not uncommon during pregnancy, and the body's response to short-term glucose fluctuations spanning limited duration such as during the later few months of pregnancy is very forgiving, though it may not be the case with the patient's predisposition to diabetes. Mid-night infusions impose inconvenience to the mother, but they truly aim in preventing early morning hypoglycemic phase that can be otherwise prevalent even in healthy pregnant women. During such short but many of hyperglycemic peaks in a day the placenta can transmit D-glucose in an exceeding ‘speed mode’ of Vmax (refer the Michaelis-Menten model discussed in the foregoing section) when the surplus of the hexose sugar is stored both as fetal liver glycogen and the placental lactate that are utilized as the circulating glucose levels tend to fall.
The management of an IUGR pregnancy clinches on the correct diagnosis of it's existence. A correct diagnosis is made by any one or all of the following—1. confirming the current gestational age as per the first trimester ultrasound, and the previously correlated uterine size, 2. the gestational age as per the CLMP which was earlier discussed, 3. any reliable previously discussed U/S indicators of true fetal gestational age.
When fetal IUGR is confirmed, the patient shall be hospitalized with decreased physical activity and bed rest, as the fetal surveillance is started. This includes fetal movement charts, clinical and ultra-sonogram assessment of fetal growth, amniotic fluid (AF) volume, non-stress test (NST), biophysical profile (BPP), fetal heart rate (FHR) monitoring, Doppler velocimetry, AF lactate/lactic acid (AF-LA) levels, and also clinical evaluation of the mother. Full profile of this exhaustive list of tests (see table-7) can be tailored to the physician's discretion, as clinically warranted.
In most cases of IUGR, as pregnancy can be quite remote from term, and fetal viability improbable (with prematurity added to growth restriction), irrespective of the base-line lab values i.e. unsatisfactory doppler velocimetry, or non-reassuring FHR/BPP, hypertonic glucose treatments are advised. As discussed, it's multifaceted effects upon IUGR pregnancy is unparalleled. The aim is to reverse pathology of whatever severity, at any stage of pregnancy. The patient needs to be disclosed that pregnancy outcome is very unsatisfactory without it, though however, as with any treatment, 100% response and assured positive pregnancy outcome may not be guaranteed, because the inclusion group is of varied pathology, some inherently unresponsive. The patient may also be informed that statistical data of the treatment is not available at the time, but it can be very promising. Clarify that there is a possibility of fetal demise with or without treatment, and hence treatment is strongly advised, as at least there will be satisfaction of trying what is feasible, and that the treatment will be continued only until fetal viability, for elective delivery.
Base line diagnostics—all baseline diagnostics are documented in the comprehensive 7 day ‘The fetal monitoring/treatment intervention table (table-7), devised for the regular outpatient or for in-hospital charting, for any needed diagnostics and for the indicated plans of intervention.
Starting the patient on IUGR diet—Special emphasis should be made that along with the diet that usually contains complex carbohydrates, intake of rapidly absorbable simple hexose sugar as 25 grams of glucose powder in water before each meal and each snack—should be a mandate of the dietary protocol. The diet also includes at least 1 egg with each meal and breakfast, for ensured essential amino acid intake (the egg being a ‘reference protein’ in terms of it's essential amino acid content, and being acceptable even for a habitual vegetarian) to ensure one of the benefits among many—the arginine supply needed for feto-placental nitric acid synthesis, for relieving placental and umbilical vascular impedance. Arginine is also an insulin-secretagogue, whose action can be preserved even when glucose stimulated insulin secretion is impaired (Powers A C). This works in favor of improving maternal glucose tolerance in those with a predisposition for gestational diabetes.
The hypertonic D-glucose is supplied by the manufacturers in a prefilled disposable syringe with optional stick-guard safety needle (MIN-I-JET) in the standard strengths of 25% (2.5 g in 10 ml) and 50% (25 g in 50 ml) solutions, as below—
The amniotic fluid lactic acid/lactate (AF-LA) level, or lactic acid/creatinine ratio (L/C ratio) as therapeutic aid in clinical decision making—AF-lactic acid levels or L/C ratio can be a tool of decision making, and can be specifically directed to finding the lactic acid level before and after D-glucose therapy, for adjusting the dose of the supplements, if there are also accompanying changes in BPP scores. With the therapeutic benefits of D-glucose on fetoplacental ATP generation/arginine transport, NO synthesis, and vasculogenesis leading to fall in placental impedance, the patients if started on O2 therapy due to elevated lactic acid levels, can be swiftly or gradually weaned off from either the intermittent oxygen therapy (IOT), or continuous oxygen therapy (COT) while D-glucose treatments are continued, as the aim is to send the patient(s) home, stabilized on an optimal but tolerable dose of DG25-50, without home oxygen therapy the latter being not feasible in all cases. With elevated AF lactate levels (>10.1 mmol/L, Pardi et al, 1987) only COT is started initially, with IV glucose therapy supplemented after the lactate level normalizes.
Any patient if resistant to IV DG25 treatment even with continuous oxygen therapy (COT), it clearly indicates significant fetal hypoglycemia due to placental insufficiency that needs to be interfered with intraamniotic isotonic D-glucose treatments. Normal or below normal AF lactic acid level clinches that the problem is hypoglycemia, with or without hypoxia.
With normal/normalized AF lactate levels, the patients are divided into following groups based on the gestational ages and the baseline BPP scores.
With normal BPP score accompanied by IUGR, it can be considered that the fetal growth restriction is mild to moderate. This fetus is obviously not acidotic, as there is a direct correlation between the BPP score and fetal acidemia. It can also be reasonably expected that the fetus tolerates hypertonic glucose treatments in moderate doses without requiring oxygen therapy in the manner it may be otherwise required with very low BPP scores accompanied by severe hypoxia. The following is the most feasible therapeutic interventional protocol for this group of mothers—
DAY-1: Start DG25 as 50 ml (12.5 g of D-glucose) thrice daily (10 am, 4 pm, and 1 am).
DAY-2: 8-9 am—check BPP. If score remains as baseline, continue same treatment on day-2.
DAY-3: increase the dose to DG50 as 50 ml (25 g of D-glucose) thrice daily.
DAY-4: 8-9 am—check BPP. If score remains same, continue the treatment on day-4.
DAY-5: if the patient is stable with no FHR changes (as described below), and with BPP score of ≧8, the patient is discharged home with the last maximal dose tolerated, to be further increased to DG50 as 75 ml thrice daily, and later DG50 as 100 ml thrice daily, as pregnancy advances.
Intermittent FHR (fetal heart rate) monitoring—it is done for four hours starting ½-1 hour before the therapy initially, and later, whenever the dose increments are made. For any adverse FHR changes, IOT (the intermittent oxygen therapy) is started with 6 L O2 by nasal cannula to be continued for 2 hours and then to be tapered every ½ hour as 6 L-5 L-4 L-2 L-stop. Weaning from IOT, or advancing to Continuous Oxygen Therapy (COT) with slow increments of DG25-50 in the latter situation, is in a manner similar to that shown in the algorithmic flow sheet for GROUP-B, in the subsequent section.
The rationale of BPP monitoring as a proxy for AF-LA/pH levels—Though the initial decision making was based on the AF-LA level, the subsequent follow up is not feasible to be solely based on AF-LA levels. Any deficit, either fetal hypoglycemia or hypoxia, by failing to generate ATP is reflected in the fall of BPP score, due to fetal hypotonia. Oxygen therapy can be added at this point to the ongoing D-glucose therapy. The physician can check AF lactic acid levels, though infrequently, when the BPP score shows no improvement with sufficiently titrated oxygen therapy.
In cases with both the FHR change, and fall of BPPS by 2 or more, at any time during treatments of DAY 1-5, as above: the FHR changes are treated with intermittent O2 therapy (IOT), as above. The thrice daily D-glucose dose can also be changed to twice daily, to be administered at 1 am and 10 am, and the response observed with further monitoring. This patient may be increased to higher dose very gradually. Other needed testing can be also incorporated, if felt appropriate. The subsequent plan is similar to the plan outlined in the algorithm flow sheet below, for GROUP-B.
Days 1, 2, 3 (or more) (for example) can be more days in the real time patient care, with unforeseen delays of response. This seeming time-line is indeed a therapeutic mode line. Numbers for the days were introduced because they are better tools of chronology, and of mutual communication in unambiguous terms. The time-line only indicates suggested minimal time, and similar plan can be continued with more time allowed for specified increments.
At the end of 1-2 weeks of hospitalization, or as needed—the fetal size is checked by ultrasound, as there will be discernable increment in fetal growth parameters by 2 weeks at times the catch-up growth more than normally expected. Such observation of response is the best prognosticative indicator compared to any other standard monitoring modalities, to continue the maternal hypertonic IV glucose treatment.
Maternal IV Hypertonic D-Glucose Treatment Protocol Algorithm for the Gestational Ages of 26-31 Weeks, and with the Baseline BPP Score ≦6 (26-31 GROUP-B)—
Algorithm Flow Sheet for Group-B, 26-31 Weeks (BPP Score ≦6): For D-Glucose 25% (DG25) Maternal Intravenous (IV) Therapy, Starting Twice Daily (1 am & 10 am), with Progressive Increments
IOT—as a routine, intermittent O2 therapy as 6 L/minute by nasal cannula is done soon after a noted fallen BPP score (to be tapered as described, after 2 hours), and again during each DG25-50 therapy, to be tapered also after 2 hours.
Intermittent FHR monitoring—in addition to BPP, intermittent FHR monitoring can be started ½-1 hour before the treatment in a similar manner as specified for the preceding group. For any adverse FHR changes, IOT as 6 L O2 is started as above.
COT/IOT weaning by Every Day Challenge (EVDC) of CAT-3—In the above protocol algorithm, for CAT-3 while trying to change COT to IOT, when every day weaning attempts (EVDC) are commenced, patient's COT is tapered starting at 6 am, with ½ hour decrements as 6 L-5 L-4 L-2 L-stop. FHR tracing response can also be observed, and recorded with FHR monitoring starting at 5-5.30 am, to be intermittently observed throughout the day, as needed. COT is switched to IOT if BPPS is maintained at least as 6. Similar FHR monitoring during oxygen weaning can be incorporated for CAT-4 management also, or at any time for any patient for additional and immediate observation of fetal response to weaning, and for charting the same. While BPP is time taking needing the presence of a physician or any specially trained professional, FHR observation is easier, and is a familiar monitoring technique to all the care-takers. Any non-reassuring tracing can be an indication to immediately restart oxygen therapy, as a standing order. Such daily monitoring needs to be continued until the patient is stabilized on a particular DG25-50 dose before discharge, with or without elected oxygen therapy. Any patient in this group or any other group if not stabilized even with continuous oxygen therapy that is tailored to the fetal response, it indicates at this point that there is significant impedance to placental D-glucose transfer, probably due to placental vascular luminal obliteration, and transamniotic isotonic D-glucose supplements are indicated as the last resort, which is discussed in detail subsequently.
With the most distressed group being CAT-3 with BPPS of 4 or less on COT, the patients of this group may need SIPP catheter placement for transamniotic isotonic D-glucose supplements, if there is no satisfactory improvement of score after 2-4 days of treatment with COT.
For BPPS of 8 or more (32, GROUP-A)—The protocol and management of complications of this GROUP is the same as the previous group (that is 26-31, GROUP-A) The group can be started with DG50 for all BPP scores. If the fetus responded to treatments with out need for oxygen, and with a BPP score of 8 or more, the treatment is continued up to 34-35 weeks to plan delivery by checking L/S (lecithin/sphingomylin) ratio for needed corticosteroid therapy. For planning delivery, along with biweekly NST/BPP, biweekly Doppler velocimetry is also helpful.
For BPPS of 6 or less (32, GROUP-B)—the mother is hospitalized, immediately started on 6-8 L/minute of continuous oxygen therapy (COT). The AF is drawn for testing of L/S ratio, lactate/lactic acid levels, and immediate corticosteroid injection done. A maternal IV infusion of all B-complex factors and minerals in maximal allowed doses is given. The effects of vitamin deficits on the most distressed fetuses are discussed in the last section ‘The neonatal care of an IUGR baby’. After the patient is stabilized on COT (which implies improvement of BPP score at least by 2 on COT), the preceeding algorithm protocol is followed (while the AF LA levels also are found in/brought to an acceptable range), until the fetus acquires reasonable weight gain, with cesarean delivery planned at 34-35 weeks. The pregnancy not being remote from term, the management of this group is not laborious. Even 32 weeks neonates are more prone for morbidity/mortality compared to their AGA counterparts, and hence allowing even few more weeks of intrauterine stay can be a saving measure.
Vascular access for glucose therapy—Once definitive fetal growth is observed, the mother is a potential candidate for continued IV glucose treatments. In view of at least 6 more weeks to pass, with prospective elective abdominal delivery soon after, a peripherally applied central venous catheter access has to be strongly contemplated, and performed before discharge, as this is the best time for such procedure. This is applicable to all groups remote from term. Simpler and modified materials and methods for such peripheral venous access is described later. The possibility of not finding a vein after few days, and remote from the time of fetal viability can be anxiety provoking to the patient, and to her care-takers as well. For patients not remote from term, and maintained on regular IV line, if the available veins are exhausted just around the time of fetal viability and before elective delivery, subclavian triple lumen central line placement can be an option for such patients.
Patient education, and maternal care by home health nurse—All the patients need to be educated about the treatment, and the strict aseptic manner under which the intravenous access has to be conducted, for the patients to continue the treatment at home. A home health nurse needs to be assigned to monitor the patient, and to attend her at home, when ever needed.
The above hospitalization of the mother with bed rest/oxygen weaning, an average of 7 days or more, should be viewed as days less than those a premature/dysmature baby may otherwise have to spend in NICU (neonatal intensive care unit), but with unpredictable outcome, despite the trauma invariably inflicted to the neonate, even in it's most hospitable and an intensely caring new world.
The transamniotic isotonic glucose supplements, and the means of amniotic cavity access, either diagnostic or therapeutic—Any patient if not stabilized even with continuous oxygen therapy (COT) that is titrated to the fetal response—it indicates that there is significant impedance to D-glucose transfer probably due to placental vascular luminal obliteration, and transamniotic D-glucose supplements are indicated as the last resort (which is discussed in detail subsequently), as unresolved hypoglycemia is certain. In addition, if AF lactic acid level is low or normal to start with and on COT, it clinches the diagnosis of ongoing fetal hypoglycemia (when serious infection/genetic fetal compromise is ruled out).
When the amniotic cavity access is one time, or more, the ‘sterile patch technique’ (devised by the author inventor) is strongly advised. It involves placing any conventionally used antiseptic patch-like skin cleaning device, like an ‘alcohol patch’ over the sterile skin puncture site of the maternal abdomen, through which the needle is inserted, while care is observed for the center of the ‘sterile-patch’ to be untouched by the injector's hand. The amniotic cavity is accessed under ultrasound guidance to avoid the placental site, while the bladder is completely emptied, to avoid inadvertent bladder entry. Uterine cramping, vaginal spotting, or fever need to be watched for. AF leak occurs in 1-2% of cases, but stops in 2-3 days. Consequential miscarriage is not common, as the amniotic membrane seals, and AF accumulates (Marion S V et al). When there is question of whether or not AF was aspirated for the required testing, the crystalline arborization test can be used. Rh sensitization is possible and anti-D immunoglobulin (Rhogam) is indicated for Rh-negative susceptible mothers, even after single amniotomy. As a general rule, a pool of AF can be accessed in the mid suprapubic area (better by upward displacement of fetal head), in case the placenta is visualized to be located elsewhere, and in this site, the separation of the recti reduces the intervening maternal tissue (Whitfeld C R, 1978), and the fetus is untouched by the needle. AF pocket can also be found by careful palpation, near the fetal limbs, or behind the fetal neck in case of breech.
1. When there is equivocal AF measurements lowering the BPP score—check the Umbilical artery S/D ratio. Patients with oligohydromnios but normal umbilical artery doppler S/D ratio are less likely to have poor perinatal outcome. With normal Umbilical artery S/D ratio, grade AF pocket measurements as score 2, hydrate the patient with 2-3 liters per day under bed rest, and reevaluate.
2. If there is doubtful fetal breathing—when there is doubtful fetal breathing with unequivocal score or lowering of the BPP score, check umbilical venous Doppler for clarification. During fetal breathing, the umbilical venous waveforms are undulating, such wave forms corresponding to fetal inspirations, with a frequency much lower than fetal heart rate.
3. Correlation of BPP with fetal blood pH—BPP score of 8-10 corresponds to fetal blood pH of 7.37 (in the normal range), and a score of 6 corresponds to a pH of 7.33, and a score of 4 with pH of 7.28 (Manning et al).
4. O2 Therapy—The uterine placental vasculature during pregnancy is unique in that it is refractory to changes in blood gas tensions (PO2 and PCO2). Therefore, oxygen therapy either due to maternal or fetal causes will not cause placental vasoconstrictive response, and hence there is no adverse effect on fetal blood flow. The fact that the oxygen demands are more for aerobic oxidation during peak blood glucose levels and such demands can be less as the levels decline, and further, the progressive alleviation of fetal hypoxia by 33+%, 400%, and 10% via different metabolic consequences, as a multifaceted response due to maternal D-glucose therapy—makes the oxygen deacclimatization tapering tolerable to the fetus.
5. CO2 production—Renewed glucose metabolism in the fetus can generate proportional amount of CO2. In the glycolysis-citric acid cycle, for the aerobic combustion of 1 molecule of glucose, 6O2 molecules are used, and also 6 CO2 molecules are liberated. That means, combined glucose-O2 utilization always generates CO2 in direct proportion. However, maternal hyperoxygenation also facilitates Haldane effect at the placental level, that is, more of O2 picked up by fetal hemoglobin also facilitates more of CO2 to be released from it, to enter the maternal compartment. Therefore, in the face of artificially and therapeutically improved fetal oxygenation (but yet with the prevailing placental insufficiency), a resultant fetal hypercarbia (hypercapnia) may not be feared. The Haldane effect can be considered as the body's evolutionary achievement as a cause and effect phenomenon in the case of life-sustaining diffusion of vital gases, the O2 vs. CO2. That is, when oxygenation improves, CO2 that may also increase in direct proportion needs to be let out, also in the same proportion as the oxygen is increased.
Continued Prenatal Monitoring of Fetal Well-being, and of Fetal Growth Parameters after the Patient is Discharged Home—
1. Uterine height: is monitored every two weeks, as a measurement in centimeters.
2. Fetal U/S: is monitored every two weeks, to affirm and document ongoing fetal growth.
3. Fetal heart tracing: is monitored weekly, or earlier if mother reported suboptimal fetal movements.
4. Maternal monitoring and documentation of fetal movements: it is done daily, for 1 hour at a stretch. 10 fetal movements count in 1 hour duration is reassuring. If were found to be less, the mother should continue counting for one more hour. If they are fewer than 10 movements in the 2 hour period, she should contact the physician. An alternate way of fetal movement monitoring is, to count them for 30 minutes at a stretch, 2-3 times daily. Normally, there should be at least 4 strong movements during each 30 minute period. Encourage the patient to maintain peaceful atmosphere at home, and to use a ring buzzer over the abdomen to startle the fetus from sleep before the 1 hour monitoring to make the results more reliable. Both the self-administered glucose treatments, and the fetal monitoring should be formally documented on a sheet provided to her.
5. BPP: it is monitored biweekly—after the patient is stabilized on optimal DG25-50 and sent home, and done earlier if mother reported suboptimal fetal movements.
6. AF-LA and L/C ratio: normal or low levels indicate unresolved fetal hypoglycemia if patient is treatment-refractory, even on COT.
7. UA and MCA velocimetry: it is monitored weekly—starting at 30 weeks, to plan or to be warned of the impeding need for fetal delivery, for possible acute over chronic declining in the placental reserve, as exponential growth in the volume of placental terminal villi capillaries occurs starting 31-36 weeks failure of which is reflected in Doppler FVW forms. The S/D ratio and PI are reliable parameters. One may not wait for manifest ‘Absent End Diastolic flow Velocity’ (AEDV), or the ‘Reversed End Diastolic flow Velocity’ (REDV).
8. AF-L/S (lecithin/sphingomylin) ratio: it is done at 32 weeks.
9. Umbilical venous Doppler: it is done any time for equivocal fetal breathing off-setting the BPP score. It has to be noted that non-reassuring venous doppler signs are late signs, as fetal heart failure and multi-organ damage are known to have already occurred, and hence not used as monitoring techniques of continued fetal well-being in this protocol.
An IUGR baby with precarious placental reserve, or maintained on intermittent or continuous oxygen therapy (IOT or COT), is rarely expected to survive the stress of labor. On the other hand, mothers who either needed no oxygen or were successfully weaned of oxygen, persistently maintained 8-10 BPP score, did not manifest olgohydromnios, and had not demonstrated RDFV in umbilical doppler velocimetry—can be tested with contraction stress test (CST) to estimate the placental reserve. If found adequate, a vaginal delivery can be tried with—continuous electronic fetal monitoring as the mother maintained on 8 L/minute continuous oxygen therapy; continuous DG5 IV fluids; the IV DG50 as per the regular timings; the operating room kept ready for emergency cesarean. With all the time and effort spent in prolonging the intrauterine fetal stay for the delivery of a well grown baby with it's best potential preserved, when the time has arrived for it's delivery, swaying in favor of a cesarean is no doubt better.
In planning immediate delivery, along with biweekly NST/BPP, weakly bi-weekly Doppler velocimetry is also helpful.
showing TCD in millimeters at 10th, 50th, and 90th percentile) in an IUGR pregnancy, and it remains consistent throughout, independent of fetal IUGR.
(b) Bony ossifications—the ossification of distal femoral epiphysis occurs predictably around 32 weeks, and that of the proximal tibial epiphysis around 35 weeks, these two noted as prominent echoes distinct from the rest. Presence of distal femoral epiphysis of greater than 3 mm, and the presence of any proximal tibial epiphysis indicate a mature lung in almost all IUGR fetuses (Galan H L, 2003).
A patient who responded to the therapeutic maternal hypertonic D-glucose treatments, as indicated by definitive ultrasonic parameters of fetal growth response, but at a gestational age remote from term, needs a secure vascular access that tends to last for an average period of 2 months. Broviac catheter that is a peripherally placed central venous catheter is an ideal tool in this situation, as it can be managed by the patient at home, without significant risk of sepsis.
The vascular access can be done via skin cut down in the anticubital fossa, and with a venipuncture preferably through the brachial vein. Different pediatric sizes of Broviac central venous catheters are available, and the appropriate size can be chosen for this purpose. The catheter was originally designed for total parental nutrition (TPN) for which the placement of the catheter tip should be at one of the larger central veins, and placement of the catheter tip as proximally as possible is advisable for the hypertonic strength of D-glucose being infused. Smaller pediatric size Broviac catheter allows placement of the catheter through the patient's forearm. Mentioning to the patient that a baby needle and a baby catheter are sufficient for the procedure instead of the adult size (after making sure that the patient may not misunderstand that it is for her baby in-utero) will reduce patient apprehension, and can improve patient-acceptance. However, it should also be clarified that it is not a simple procedure like the regular peripheral venous access that people are mostly familiar with.
The Broviac catheter is made of soft radiopaque rubber, with a small Dacron felt cuff at a specified distance from the external end. The internal diameter is less than 1 mm for the pediatric sizes, and the catheter consists of a thin walled intravascular segment and a thick walled extravascular portion. The extravascular portion is tunneled through the subcutaneous tissue to a separate skin exit site, distant from the venotomy site. The Dacron cuff is so located in the catheter that it will be positioned within the subcutaneous tunnel, and the fibrous tissue ingrowth into the cuff acts as an effective barrier to the bacteria possibly migrating from the skin into the venous system along the outer surface of the catheter.
Technique of placement—Though typically the catheter is placed by venous cut down, it can also be placed in a manner similar to subclavian central venous access, using a guide-wire (the Seldinger technique). The patient's left forearm is chosen for a right handed person, so that the patient can self-inject. As the chosen catheter entry site is the anticubital fossa (where the scar can merge with the ante-cubital crease), the catheter exit site can be somewhere on the medial aspect of the forearm, where it is less obvious, yet can be easily cared for, by the patient.
To start with, an appropriate size pediatric subclavian central venous access kit should also be procured along with the pediatric Broviac catheter. A small cut (of 1 cm) is made in the skin, over the proposed venipuncture (venotomy) site. As the cubital veins are very superficially located, it is better to lift a skin fold, cut with scissors, and widen the skin incision to the desired length (avoiding the scalpel contact with the superficial vessels throughout). From there a subcutaneous tunnel is made to the chosen skin exit site on the medial aspect of the forearm. When the tunneling instrument approaches the skin exit site, a small incision, about 1 cm, is made at the skin exit site. The tunneling instrument at it's exit picks up the catheter tip to be brought to the venotomy site, while retreating in it's course. Then the brachial vein is entered through the needle supplied in the triple lumen kit. The brachial vein can be seen or located by brachial artery palpation. Using a guide wire and a vein dilator, the Broviac catheter tip is threaded into the vein through the guide wire, in a similar manner that a subclavian central vein catheter is placed, as in the Seldinger technique. The catheter is passed into one of the central veins or their largest distal veins to a distance that allows the Dacron cuff to be positioned in the patient's forearm inside the subcutaneous tunnel. The venotomy site incision is closed, and the catheter is fixed to the skin exit site by mono-filament nylon that is removed after 1-2 weeks by which time fibrous ingrowth into the Dacron cuff has taken place. Sterile povidone iodine ointment and a sterile dressing are applied to the exit site, and the catheter is filled with heparin treated saline, and closed with hep-lock. The loop of the redundant catheter if any is taped to the medial aspect of the forearm.
The patient has to be advised that even the hep-lock needs to be cleaned with a povidone iodine ointment, and after use, covered with sterile tape seal, so that the hep-lock is kept clean, what ever be the patient's activity. The hep-lock has to be injected with sterile gloved hand through any sterile skin patch, like an alcohol patch, placed over the hep-lock. The hep-lock is changed more frequently in view of the long catheter in-dwelling time, and hence needed stringent care. The extracutaneous redundant part of the catheter is also cleaned with the ointment, and taped to the hand by sterile adhesive dressing. The procedure being least traumatic and least invasive, it is easy to gain patient acceptance, as it is essentially like any simple peripheral venous catheter placement, with least injury to the vessel wall, and in addition, with a devised protection against sepsis, for the needed indwelling time. Ideally, the catheter placement is done in the controlled environment of an operating room, under aseptic precautions.
If the physician has not found any suitable tunneling instrument in the armamentarium of the available surgical tools, to use in the small curvilinear confines of the fore arm, as aesthetics are also essential in an exposed anatomical site like the fore arm of an young female, the author inventor of this writing advocates to use a Hegar cervical dilator (or a Hank cervical dilator) for this purpose. It's smooth and delicate curvilinear sigmoid shaped structure suits the contour of the fore arm, with the smallest size having 21 cm length, and 3-4 mm diameter (half of the dilator is 3 mm diameter, whereas the other half has 4 mm diameter) (Gynex), and rough manipulations invariable with other instruments in this area, can be avoided. It can also make the needed incisions to a minimum size. However, the procedure needs some modification (as in Sumathi Paturu's subcutaneous tunneling technique for venotomy). It can be done in the following manner, using also a straight urinary catheter as a passage sheath.
Sumathi Paturu's subcutaneous tunneling technique for venotomy—To start with, the sterile Hegar dilator is passed into a suitable size sterile straight rubber urinary catheter, and so enclosed, the catheter tip can be negotiated through the venotomy incision site to the skin exit site located distally on the medial aspect of the fore arm. Following the exit of the tunneled instruments at the distal skin exit site, the instruments can be gently moved side to side (not rotated on their axis), so that a wider and suitable caliber subcutaneous tunnel is created, as it needs to accommodate the Dacron cuff. Soon after, the Hegar dilator can be removed retreating through the venotomy site, leaving the sheath of urinary catheter in place in the subcutaneous tunnel. The urinary catheter tip can be cut to expose it's whole caliber at the skin exit site. From this widened cut end, the tip of the Broviac's catheter can be passed to reach the venotomy site in the anticubital area. After the exit of the tip of the Broviac's catheter from the urinary catheter end, the urinary catheter can be removed over the Broviac's catheter, which it had enveloped. It is done from the venotomy site. It can be noted that only the tip and the proximal length of the Broviac's catheter has to pass through the urinary catheter. If the creation of the tunnel poses a problem, a curved hemostat or curved scissors can be used to separate the tissues, and to create the needed cleavage in the subcutaneous planes, but approached from both ends of the tunnel separately, as one straight plunge can make a curvilinear negotiation difficult, as only the tip of these instruments is curved for a confined length. In a very lean person, or if the exit site is chosen on the anterior aspect of the fore arm, the tunnel can be relatively straight, and most of the instruments are suitable in this situation though a hinge in an instrument always makes it wider, and can never be as the ideal small caliber of a Hegar/Hank dilator.
The size of the urinary catheter is chosen in such a manner that it's movement over the Hegar dilator is easy, but the fit not too loose. Leaving the tip as it is, the catheter can be cut at the other end to start with, to use only the needed length for this purpose, that is, 1-2 inches longer than the curvilinear length of the proposed subcutaneous tunnel. This procedure is suitable for any subcutaneous instrumental tunneling and venotomy, for any regular catheter or for any port-catheter placement, in any preferred venotomy site.
Further precautions that can be observed to prevent infection of the catheter is—antibiotic lock technique, that was used successfully in the medical field, to treat and prevent central venous catheter infections. The technique involves injecting an antibiotic solution (preferably Vancomycin 2 mg/ml) into the catheter lumen, and allowing the antibiotic to sit in the line for at least 12 hours, before surgically inserting it into the patient. The catheter is periodically reinjected and the antibiotic is made to sit in a similar manner, after clamping the catheter at the skin entry site. It has to be done after completely emptying the blood column from the redundant catheter by antibiotic injection, before clamping the catheter at the skin entry site, and allowing the antibiotic solution to stand in the redundant catheter lumen until the time of the next D-glucose injection. It prevents the possible infection introduced into the interior of the catheter lumen during the daily use, which the Dacron cuff may not prevent. Vancomycin, like penicillin, is pregnancy category-B.
The biochemical benefits attributable to normoglycemic status of the fetus, possibly achieved by the additional modality of the transamniotic isotonic D-glucose (DG5 isotonic, or D5 water) treatment is similar to what was elaborately discussed under the section of ‘Maternal intravenous hypertonic D-glucose supplements’. However, being an invasive procedure, though minor in nature, it is advised as the last modality of treatment when all else fails, including the concomitant continuous oxygen therapy (COT) with the maternal IV hypertonic D-glucose treatments. No improvement of BPP score during increments of maternal D-glucose therapy while on COT clinches the diagnosis of ongoing fetal hypoglycemia due to severe placental impedance. The transamniotic D-glucose supplements being not therapeutically all-inclusive in relieving the fetal growth restriction, the placental supplies of D-glucose through maternal treatment should be ongoing, and paramount. Normally the placental glucose requirements are more than the fetal, as the placenta extracts 50-60% of glucose entering maternal sinusoids for it's multitude of functional requirements, the most important being supplying glucose to the fetus in the form of lactate, when transfer of D-glucose from the maternal compartment itself is low, as during maternal sleep cycles/maternal fasting.
Despite a last resort, nutritional supplements via amniotic fluid (AF) is scientifically an attractive proposition. The phenomenon of intrauterine fetal swallowing is taken advantage of in this modality of treatment. 5% of isotonic D-glucose solution can be safely instilled into the amniotic cavity without adversely affecting osmotic forces. 5% D-glucose which is isotonic with maternal extracellular fluids should be isotonic with the AF, because the normal osmolality of the maternal plasma and the fetal plasma are in the range of 260-275 mosm, and so also is the osmolality of AF from 20-30 weeks. Instillation of 100 cc of 5% D-glucose twice daily is a supplementation of 10 G. of glucose that would amount to 41 kilocalories of energy supplement to the fetus, and it can be administered thrice daily (62 kilocalories) or four times daily, as the pregnancy advances. Even if AF is replaced every 3 hours, still substantial amounts can get into the fetal body.
Studies of transamniotic fetal feeding (TAFF) of pregnant rabbit models were conducted by Mulvihill et al in 1985 using 10% dextrose solution which had been associated with increase in fetal weight. However, studies of Flake et al with solutions of dextrose, amino acids, and of lipids, either alone or in combination did not reverse growth restriction in the natural runt rabbit fetus. The reasons for these controversial results can only be postulated. Too much of dextrose without required vitamins (especially of the B-complex factors like thiamine) needed as cofactors for the carbohydrate metabolism (presuming that the rabbit's biochemistry is similar to human) could be overwhelming to the fetus. Too much of lipid or of amino acid supplements with or without glucose can be a stress to the oxidative machinery of the fetus, the beta oxidation of fats, and the amino acid catabolism for energy-yielding purposes being oxygen/ATP consuming path-ways. It can make the existing hypoxia worse, and the co-administration of glucose not very beneficial. The concomitant maternal treatments that include prior IV supplements of vitamins/minerals, and also the IUGR diet with maximal daily supplements of vitamins, minerals, and of trace elements will compliment and make the transamniotic fetal treatments fulfilling, as the maternal route appropriately relies upon treating the fetoplacental unit as a whole. The AF 5% D-glucose supplements further improve voluntary fetal swallowing because of the improved taste, as in the research studies a new born seemed very discriminative in preferring oral sugar solutions (Johnson P & Salisbury D M).
The AF contains the valuable constituents as shown in the table-9 that had been proved to be essential for optimal fetal growth.
As the daily puncturing of amniotic sac is replete with dangerous sepsis for the needed duration of the treatment involved in human pregnancy, the invention contemplates to achieve such daily transamniotic access through a Subcutaneously Implanted Pregnancy Port Catheter (SIPP catheter) placement accomplished through a minimally invasive extraperitoneal (from outside of the peritoneum) suprapubic amniotomy. There is least danger of infection, and great ease of daily use, after it's one time insertion.
The novel transamniotic insertion of the Subcutaneously Implanted Pregnancy Port with catheter (SIPP catheter)—The novel procedure of the extraperitoneal suprapubic transamniotic port-catheter placement is tailored for obstetric purposes, and is devised by the author inventor, while the subcutaneously implantable (intravenous) catheter with port was originally devised decades ago by past inventors for exclusive use through the intravenous route. The catheter part of the device of the instant specification is also modified by the author inventor to be suitable for transamniotic approach of the amniotic cavity, and is also configured to relieve malfunctions unique to the milieu. The port, however mostly retaining it's original structure as was devised, can be used safely through the long duration of pregnancy, encompassing a ‘sterile-patch technique’, also devised by the author inventor, to make it's use sepsis-free, the introduction of infection into the amniotic cavity being a much feared complication inherent to countless number of port punctures involved.
The sterile patch technique for transamniotic infusion of isotonic D-glucose—as was described in an earlier section, it involves placing on the well cleaned (port) puncture site of the maternal abdomen, any antiseptic patch-like skin cleaning device, like an ‘alcohol patch’, without touching the center of the patch, through which the amniotic cavity can be accessed using a straight needle. The corners of the patch can also be carefully taped for a stable placement.
The access site of the amniotic cavity, for the extraperitoneal transamniotic SIP port catheter placement—As a general rule, a pool of AF can be accessed in the mid suprapubic area (by upward displacement of fetal head), in case the placenta is visualized to be located elsewhere. The separation of the recti reduces the intervening maternal tissue (Whitfield C R, 1978), and it virtually eliminates fetal injury, as the fetal body as a whole is out of reach. If the mother is kept in Trendelenburg's posture for few minutes, it also allows the cord to settle in the upper uterine pole, when the mother can be brought back to the supine position, with a slight leftward tilt for surgery.
The Structural and Functional Description of the Subcutaneously Implanted Pregnancy Port (SIPP) with Catheter—
The diagrams used to illustrate the design of the SIP port with catheter are not necessarily drawn to scale, and are shown in
The SIP port and the catheter—The SIP port is devised as a subcutaneously implantable port (200) with a housing reservoir body (201) containing a dome or diaphragm shaped septum (202) (
The reservoir body (201) is connected to a catheter (208) in the quadrant devoid of aperture, through a port stem or segment (210), and a locking collar (203). The stem or segment (210) that couples the port (200) and the catheter (208) is made of similar material as the catheter (208), whereas the locking collar (203), devised as an extension of the port (200), is made of a similar material as the port body (201) itself. The catheter (208) is made of polyurethane, with an internal diameter of 0.89 mm, and a length ranging 50-70 cm, though higher dimensions are not precluded. It's intrauterine portion is thin, and the rest, especially the extrapelvic portion is thicker in the substance thickness of it's walls. Maternal abdominal dimension vary widely. Hence a wide range of lengths are devised to be available. The length further accommodates for the fluctuating size of the bladder, and for the enlarging size of the uterus through pregnancy. The SIPP catheter has a distinct distal end and a distinct proximal end that are further described as follows—
The distal end of the catheter—The port unit (200) connected to the catheter (208) through port stem or segment (210) is actually a small off-shoot of the catheter (208) from it's distal end (214), as shown in the
The catheter (208) distal to the port segment (210) has a length of 2-3 cm that is configured as a distal segment (220) of the catheter, with a detachable silicone rubber trumpet-like terminal (222) 1 cm in it's largest diameter (with plastic underlay except under the terminal flat sheet), and structured like a hep-lock device capable to be punctured with a 18-19 gauge needle, as a means of passing a guide-wire through the catheter length. Said guide-wire is passed into the catheter lumen to relieve any block (by the amniotic fluid solid components), not relieved by infusions through the catheter, of the isotonic D-glucose with the force of a bolus. The guide-wire used for the purpose of inserting the catheter (208) initially is saved, autoclaved, and used for this purpose, if necessary. An additional trumpet (222) is supplied in the set, in case the trumpet leaks, due to punctures involving an 18 gauze needle. Such leaks can be identified by a local swelling. The distal trumpet segment (220) and the detachable trumpet (222) configured to be the direct continuation of the catheter lumen, enable the guide-wire's passage easy and uninterrupted. The trumpet (222) joint with the trumpet segment (220) is a tight threaded coupling that prevents dislodgement of the connection. As the extrauterine catheter (208), especially the distal end (214) being much thicker with a substantially larger lumen also, blockage by amniotic fluid particulate matter is not an occurrence in the distal catheter (214), including the trumpet segment (220), and the port segment (210).
The proximal end of the catheter and the catheter cuff—The proximal part (236) of the catheter (208) is shown in
The accessory parts—The SIP port and catheter set has accessory parts integral to the function of it's insertion, in a manner that are required of the conventional Seldinger's vascular access technique, except that it is done through the uterine puncture site instead of a venotomy site of the conventional procedure. The accessories include a puncture dilator (similar to a vein dilator) with 0.89 mm of internal diameter, and a guide-wire made of steel having 0.64 mm diameter, and a length ranging 55-75 cm. The guide-wire is made in the conventional manner, comprising of helical wire coils over a core of straight solid wire, with a good column strength, and can be easily bent in a manner needed for the purpose of catheter insertion. The set uses regular needle, size 18-19, but the needle is longer (8-10 cm length), similar to a spinal needle.
The Surgical Technique of the Placement of the Subcutaneously Implanted Pregnancy Port (SIPP) Catheter with Emphasis on the Related Pelvic Anatomy—
The anatomical description of the pelvis is invariable to understand the surgical procedure for the suprapubic transamniotic placement of the extraperitonelly inserted SIP port. The pelvic anatomy in the ensuing description is what is normally encountered in the non-pregnant female, and is so preserved through pregnancy.
The structural description of the pelvis-abdomen and the subsequent narration of the surgical procedure are done in the anatomical position, the conventional manner. All the drawings are illustrated in erect right sagittal/median view to relate/orient unambiguously to the organ descriptions narrated in the conventional erect anatomical position. This refers to a surgical illustration also (
As seen in the
The surgical procedure for the placement of the SIPP catheter is planned as elective surgery. The placental position is confirmed to be in the upper uterine segment prior to surgery. The patient will be started on IV D5 W at 84 ml/hour, and inserted with an indwelling Folley's catheter the night before. The Folley's catheter end is clamped and taped to the patient's thigh facilitating the catheter bulb to remain in position occluding the internal urethral meatus, so that the bladder distends to about 4-5 cm above the pubic symphysis. The patient rests in left lateral position, and is mildly sedated to blunt her discomfort.
For the surgery, the patient is made to lie in a supine position with a slight left lateral tilt, maintained throughout. In a right handed patient, the SIP port is placed over the right side of the abdominal wall, so that the patient will be able to self-inject. An area just medial to the right anterior superior iliac spine is a suitable site to create the port-pocket, as it's distension during pregnancy is minimal so that the port will be stable in it's position. As the largest dimension of the port is about 2.5 cm in diameter, a skin incision about that size is appropriate to insert the port into it's subcutaneous port pocket (hence forth called as port site). To start with, a 1 cm incision is made at the port site. To create a sub-cutaneous tunnel, a suitable size Hank cervical dilator available in 19.2-26.9 cm length range (Gynex), and a wide variety of small diameter sizes is used. It is sigmoid shaped with a smooth curvilinear configuration that can be easily negotiated over the convexity of the maternal abdomen. To start with, a preferred small diameter size Hank dilator is ensheathed in a suitable sized straight urinary catheter that allows free movement of the dilator within the rubber sheath. The ensheathed Hank dilator then is inserted through the 1 cm skin incision at the port site, and passed through the subcutaneous plane of the lower anterior abdominal wall, to course towards the pubic symphysis (hence forth the symphysis site). A sharp scissors can be used at the port site to create a plane of cleavage in the subcutaneous tissues.
A 2.5 cm (1 inch) transverse suprapubic incision (122,
If the maneuver is difficult, the course of the tunneling Hank cervical dilator sheathed in the urinary catheter (and later the SIPP catheter also sheathed in the urinary catheter), can be interrupted in the midway (at the mid-inguinal area), and brought out through a small skin incision, to repeat similar procedure as started at the port-site, for the tunneling instruments to reach the symphysis destination.
The 2.5 cm skin incision (122) at the symphysis site can be extended to 4-5 cm if necessary in case of an obese abdomen. The exposed rectus sheath is cut vertically as much as possible, when it may be noted that the peritoneum of the lower abdominal wall is not encountered, and further more, the distended and bare upper part of the bladder (114), also devoid of the peritoneal covering (116) is immediately underlying the cut rectus sheath (
The fetal head (130)/the presenting part is displaced upward, and held in that position by an assistant. The patient can also be kept in Trendelenburg's position, if loops of the umbilical cord (132) are visualized at the lower uterine pole (as seen through the ultrasound equipment), so that they will settle towards the opposite pole. The patient is then slowly put back to horizontal position, with the fetal head (130) still held up by an assistant. The 18-19 gauze amniotomy needle provided in the SIPP catheter kit, along with a syringe (134) is now inserted to traverse through the lower uterine segment (128) to reach the amniotic fluid pocket (136) below the fetal presenting part. Clear white amniotic fluid fills the syringe (134). The 18-19 gauge needle can be moved gently in a wider circular motion to dilate the uterine puncture site (allowing more of myometrial, and less of amnion puncture to dilate), which maneuver is better than introducing another instrument like a puncture dilator which can widen the amniotic membrane puncture with the chance of amniotic fluid leak at this site. The amnion being a delicate membrane, it can easily yield to the passage of the soft SIPP catheter over a guide-wire, and hence minimal instrumental maneuvers through it are better. At this time, the guide-wire provided in the SIPP kit is introduced into the amniotic cavity through the needle, and after sufficient length of the guide-wire is in the amniotic cavity, the needle over it is removed. Following it, the distal end of the guide-wire is passed through the proximal part (236) of the SIPP catheter (208) that was already brought to the amnitomy site. As most of the catheter (208) in this situation is not free, and is located in the subcutaneous plane, it is the passage of the guide-wire into the catheter (208)(and not vice versa) that needs to be accomplished until the guide-wire is felt at the distal trumpet segment (220) that is opened now by disarticulating the trumpet (222) to let out the guide-wire, when also the SIPP catheter (236) tip is passed into the amniotic cavity over the guide-wire, as the let out trumpet end of the guide-wire is secured by hand. Following it, with sufficient length of the catheter (236) within the lower uterine segment, the guide-wire is completely let out through the opening of the trumpet segment (220) in a swift motion (while the catheter entry into the uterus is also steadied), and the trumpet (222) is quickly articulated with it's trumpet segment (220), not to allow too much of amniotic fluid leak. The trumpet segment (220) being configured as the direct continuation of the linear length of the catheter, the guide wire's exit is made easier and uninterrupted from this route. The amniotic cavity can be immediately injected with 50-100 cc or more of isotonic 5% dextrose, to replace the lost volume.
A 5-10 cm of intrauterine length of the SIPP catheter (236) is required. A red mark on the proximal catheter (236) delineates this length. The cuff (226) of the catheter stabilizer (224) is encircled around the proximal SIPP catheter (236) out side this red mark, and is secured (glued) to the SIPP catheter exterior with a biocompatible adhesive (epoxyamine or the like). The apertures (230) of both the cuff wings (228) are sutured to the superficial muscular layers of the lower uterine segment (128) so that the catheter will not be dislodged, nor the intraamniotc catheter (236) length lowered. The retractor (120) keeping the peritoneal shelf (124) away from the bladder (102) is now removed to let the peritoneum (124) fall back to it's position in the pelvis (106). About 10-15 cm of redundant length of the SIPP catheter (208) within the extraperitoneal pelvic space is sufficient to allow for the uterine rise and the bladder distention. The incision (122) is closed in layers, while allowing the SIPP catheter (208) to stay in the subcutaneous and extraperitoneal planes, traversing from the port-site to the amniotomy site.
If the lower uterine segment (128) devoid of peritoneum is not visualized, it indicates that the posterior utero-vesicle fold of peritoneum is still attached low down to the lower uterine segment (128) when one may see two layers of the peritoneum covering the lower uterine segment (128), as the peritoneum is separated from the superior surface of the bladder (114) through the incision (122). The anterior fold represents the peritoneum separated from the superior surface of the bladder (114), whereas the posterior fold is the posterior part of the uterovesical fold of peritoneum, the peritoneum that normally covers the lower uterine segment (128). If such situation is encountered, make a small transverse incision 1-2 cm size over both the peritoneal layers, pass a suitable size straight urinary catheter between the myometrial wall of the lower uterine segment (128) and the posterior fold of the cut peritoneum, and let the urinary catheter be maneuvered down to reach the uterovesical junction. This can be accomplished by rolling and/or side to side movement of the urinary catheter with a tip sufficiently tough for this maneuver. The straight urinary catheter is picked up just anterior to the reflection of the uterovesical fold of peritoneum, this step also aided by finger guidance of the surgeon. If visualization is needed, a culdoscope is a suitable instrument in this narrow retropubic space. The proximal end (236) of the SIPP catheter (208) (brought to the symphysis site earlier) can then be introduced through the urinary catheter tip that is cut and widened, so that the proximal SIPP catheter (236) can reach the lower uterine segment (128) retroperitoneally, passing through the urinary catheter that ensheathed it. It is brought out through the cut peritoneal opening emerging from the urinary catheter, when the urinary catheter itself is removed retreating it's course over the SIPP catheter (236). Now the proximal SIPP catheter (236) is introduced into the amniotic cavity by amniotomy in a manner similar to the above described technique, using a 18-19 gauge needle, and a guide-wire.
After the cuff (226) of the attachable stabilizer (224) is glued to the proximal SIPP catheter (236) and the wings (228) sutured to the myometrium with non-absorbable sutures, both the layers of the cut peritoneum are sutured separately with an absorbable catgut, the posterior layer sutured first, and then the anterior layer. Following it, the retractor (120) holding the peritoneum (124) is removed. Now the SIPP catheter (208) is located completely extraperitoneally within the pelvis (106). Leaving sufficient redundant catheter (208) length of 10-15 cm within the extraperitoneal pelvis (106), the incision (122) is closed in layers.
Soon after the completion of the procedure at the amniotomy site, the port-site incision is extended to 2.5 cm size, and the distal SIPP catheter (214) structures, the trumpet (222), and the port (200) are inserted into port-pocket, and the port (200) sutured to the tissues with a non-absorbable material passed through the three apertures (234) of the port (200).
If the uterus can not be approached interiorly, it can be approached obliquely at an angle 45 degrees from the midline sagittal plane. When the bladder is distended, the uterus is peeled off it's peritoneal covering over some area on it's anterolateral surface, due to some separation of the anterior fold of the broad ligament. Ultrasound guidance is absolutely essential for targeted entry of the needle. Giving the patient pyridium before surgery can make the urine color orange, and the previously emptied urine can be saved to refill the bladder again during this tangential uterine approach. If entry into the amniotic cavity is confirmed through a percutaneously inserted 18 gauze needle, a guide-wire is introduced, and the needle removed. Following the guide-wire track, the uterus is approached through a small incision in the anteriorolateral abdominal wall (similar to a Grid iron incision). If the bare area of the uterus is not delineated, there can be two layers of peritoneum anteriolaterally, just as it was encountered through suprapubic approach. The bladder can also be distended more to widen the bare area of the uterus. As the pelvic floor is roomy, it is easier to reach lower uterine segment using a straight urinary catheter, as was done in the suprapubic approach, also using culdoscope if necessary, followed by transamniotic SIPP catheter insertion over the guide wire. The proximal SIPP catheter (236) is brought to this site from the symphysis-site traversing the subcutaneous plane.
The antepartum and intrapartum management of the patient treated with D-glucose transamniotic supplements are similar to what was already described under the section of maternal IV hypertonic D-glucose treatments, as this is only an additional treatment to the on-going maternal IV D-glucose supplements. CAT-3 with BPPS 4, on 6 L of continuous O2 therapy (COT) is the most distressed group of the algorithmic protocol, and the score showing no improvement in 2-4 days is the end point at which placement of the SIPP catheter is contemplated. An elective Cesarean section, as soon as the fetus is viable is indicated, when the SIPP catheter is removed from it's uterine attachment, and the port removed from it's subcutaneous port pocket.
The anaerobic metabolism of glucose secondary to chronic hypoxic insults if becomes significant in fetal IUGR, lactic acidemia can progressively threaten the fetal existence in-utero. Huang et al (1999) and Rishi Kant O et al (2006) conducted studies of normal neonates, and those who sustained acute/chronic perinatal insults of hypoxia/asphyxia as fetus neonates, with resultant neonatal Hypoxic Ischaemic Encephalopathy (HIE). They studied the very first urine samples excreted within 6 hours after birth that presumably reflected the blood/urine chemistry after the hypoxic insult had resulted. Though creatinine excretion depends on glomerular filtration rate, and is reduced during fetal hypoxia/asphyxia, lactate continues to be excreted, with it's level reflecting in the AF that is mostly composed of fetal urine (Rishi Kant et al).
The most recent and the only study of it's kind was done in Netherlands by Torrance H et al that involved AF lactate measurements, as a reflection of fetal hypoxia. This study measured AF lactate creatinine ratio (L/C ratio) that enables normalization of the concerned AF lactate values when AF volume is variable as in oligo-hydromnios (IUGR), or polyhydromnios (diabetes). The study involved term, and preterm IUGR pregnancies. Arterial umbilical cord blood and the AF were collected simultaneously during cesarean delivery. The study inferred that the L:C ratio in general decreased with increasing gestational age, and that there was no correlation to the arterial cord blood lactate and the AF lactate, but there was statistically significant correlation between the arterial cord blood lactate, and the AF-L/C ratio for the reason that the latter value enabled normalization of AF lactate values despite the variable and unpredictable AF volumes.
The inquiry is important in the optimal neonatal care of the IUGR fetus, as the care of such baby is a continuum that may not terminate abruptly at delivery. Soon after delivery, even the previously hypoxic fetus neonate starts to oxidize lactate to pyruvate aerobically, when NAD+ is reduced to NADH+H+ in many tissues of the body, and the pyruvate can be aerobically oxidized further in the citric acid cycle. If the neonate is deficient in thiamine (a co-factor needed to oxidize pyruvate to acetyl-CoA that continues into the citric acid cycle, as discussed before), as thiamine stores are usually limited even in normal adult, the lactic acidosis will simply change into pyruvic acidosis, that is no better, but it can still abruptly change/reduce the urine lactic acid/lactate level though the acidosis itself is yet to be resolved. Accordingly, an invariable fall of blood lactate can be reflected in the admixed urine.
It is imperative that as soon as delivered, the hypoxic baby, apart from being treated with oxygen, should be given thiamine and magnesium IV, proportional to the body weight, to ensure rapid resolution of lactic/pyruvic acidosis. Magnesium is a necessary co-factor in glycolysis/citric acid cycle, as essentially in all reactions in which ATP is a substrate, the true substrate is Mg2+-ATP, as the Mg2+ diminishes the dense anionic character of ATP, for it to be functional (Martin D, 1983). If intrauterine lactic acidosis was diagnosed before delivery, immediate neonatal glucose supplements may not be needed, as the pyruvate generated after the entry of supplemented glucose into the cells can compete with the conversion of existing lactate to pyruvate. When hypoxia is instantly resolved after the first breath, the blood lactate is expected to be converted to pyruvate, as specified, which then enters the citric acid cycle, when the essential co-factors (like thiamine) are also present (unless the baby is neither breathing well, nor artificially oxygenated). Even in a normal adult, after a period of anaerobic metabolism, when oxygen is available, the reversible chemical reaction that forms lactate through lactate dehydrogenase (see
Supplements of phosphorous is equally needed for the pivotal role it plays in oxidative phosphorylation, the ultimate step in the aerobic oxidation of pyruvate within the mitochondria. The phosphate group that is added to ADP to form ATP is in fact derived from the inorganic
phosphate (H2PO4−) (the hydrogen phosphate) (see the section oxidative phosphorylation). It has to be noted that oxidation and phosphorylation are tightly coupled (Mayes P A) within the mitochondrial respiratory chain, and without concomitant phosphorylation, there is no catabolic oxidation of pyruvate, or it's subsequent intermediates of the citric acid cycle.
Optimal nicotinic acid levels are so essential to the neonate as the co-enzyme nicotinic acidadenine dinucleotide, the NAD+, ubiquitous in all cellular activities, is synthesized from this B-Complex factor. A malnourished fetus-neonate deficient in needed vitamins and minerals can not be adequately resuscitated without correction of such deficits.
Though a significant correlation was found between urine L/C ratio, and the occurrence/severity of HIE (with IUGR/SGA babies as a subset of infants in this group) for diagnostic considerations in the foregoing studies, monitoring the blood lactic acid/pyruvic acid/keto-acids is valuable in these neonates for therapeutic considerations, as failure to rapidly resolve blood lactic acidosis/pyruvic acidosis/ketoacidosis especially in a SGA neonate that was chronically malnourished and hypoxic in-utero, can be reflective of vitamin/mineral deficiency. A multivitamin mineral supplement is indicated to this subset of infants (as biotin, riboflavin and pantothenic acid are also involved for the operation of citric acid cycle) to organize the whole metabolic chaos that is invariable after their prolonged stay in a depriving and hostile uterine habitat. Once citric acid cycle is set to be operative and is sustained, the multifaceted pathology of acidosis will resolve, without further clinical intervention in this regard
The pyruvate (originating from lactate) entering citric acid cycle relieves acidosis by a ‘triple effect’, that is, by oxidation/elimination of excess lactate/pyruvate, resolution of ketoacidosis, as well as generation of bicarbonate, the citric acid cycle being the major generator of CO2/bicarbonate, as the needed blood buffer base (in case the fetus is already not in hypercarbia/hypercapnia that can prevail with oligohydromnios). Hence, the persistent acidosis in the SGA neonate is due to continued lactic acidosis/pyruvic acidosis/keto-acidosis as well as lack of bicarbonate reserves, the etiology being common for all, that is the vitamin and mineral deficiency, either singly or in any combination. Glucose has to be administered with caution, while provision is given for resolution of lactic/pyruvic acidosis, when high lactate/creatinine ratio was identified in the AF, and excess blood lactic acid/pyruvic acid levels are identified in the neonate. Obviously in these fetus-neonates with high lactate levels, hypoxia is far distressing than the hypoglycemia, with or without vitamin/mineral deficits. The real life-saving measures through the perinatal period are—positive pressure O2 therapy if the infant's breathing is not optimal, and correction of vitamin/mineral deficits. One may not wait for the blood vitamin/mineral reports to arrive, for supplementing them. They have to be given into the cord blood (while the blood is also drawn for lactic/pyruvic acid levels, and other needed blood chemistry) as soon as the cord is clamped, and while the baby is resuscitated, as finding a vein later can be time taking and distressing, apart from being an unduly delayed maneuver. The umbilical vein and the ductus venosus constrict immediately after birth, but typically close in 1-3 hours after birth, and the
umbilical arteries obliterate in 3-4 days. Sodium bicarbonate is also very useful for immediate relief of acidosis. Glucose supplements should be considered as soon as the pyruvate/lactate levels are found to be falling and approaching the normal range.
It is the aim of this invention to restore all IUGR/SGA afflicted fetuses/babies to their innate growth potential and optimum health, before and after they arrive into their terrestrial world.
This concludes the specification.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10460170 | Jun 2003 | US |
| Child | 13815468 | US |
