PROJECT SUMMARY Approximately 1 in 10 babies are born prematurely each year in the United States, and these neonates are at heightened risk for acute morbidities and early death. While medical advancements have dramatically improved survival for infants born prematurely, survivors, especially if born very preterm (< 30 weeks gestation) have an increased risk for long term neurodevelopmental impairments. Bronchopulmonary dysplasia (BPD), the most common neonatal morbidity among preterm infants, is a risk factor for future chronic diseases and neurodevelopmental impairments. How BPD and its treatments lead to long-term negative health outcomes requires further study. Altered programming of the HPA axis, which modulates glucocorticoid (GC) activity, has been implicated as one potential mechanism, because infants with BPD are more likely to have been exposed to corticosteroids and BPD itself may activate the stress response system. Others have developed a cross-tissue polyepigenetic predictor, an algorithm that uses DNAm levels at specific sites on the genome, to estimate a score that is associated with exogenous and endogenous GC exposure, which has been associated with maternal anxiety and depression throughout pregnancy and with later mental and behavioral issues. However, this potentially useful biomarker has not been studied within infants that were born very preterm with BPD, who are more likely to have elevated exogenous and endogenous GCs and are at increased risk of neurodevelopmental impairments. To address this gap in our knowledge we aim to 1) investigate whether BPD is associated with neonatal GC scores (as risk factor, and as a response), and 2) examine whether the neonatal GC scores are associated with performance on neurodevelopmental assessments at 24 months corrected age, in two ECHO cohorts of infants that were born very preterm (NOVI and ELGAN). These analyses will provide evidence as to whether this epigenetic biomarker is associated with BPD, and will elucidate whether the GC scores may be an early indicator of children that are at increased risk for impairments. 1