Supplementary Material for: Association of umbilical cord blood serotonin levels with neurodevelopmental outcomes

Introduction Serotonin (5-hydroxytryptamine, 5-HT) plays an important role in early development and fetal 5-HT has been reported to arise from placental and maternal sources. Previous human studies have established an association between maternal 5-HT levels and neurodevelopmental outcomes in populations with autism. In this study, we analyze umbilical cord blood and placental 5-HT levels at birth to further investigate the relationship of gestational 5-HT levels with birth outcomes and offspring cognitive development. Methods Participants were enrolled in the Safe Passage Study conducted by the Prenatal Alcohol and SIDS and Stillbirth (PASS) Network. Infant cord blood and placental samples were collected post-delivery, and 5-HT levels were measured using high-performance liquid chromatography-fluorometric (HPLC-F) analysis. The Mullen Scales of Early Learning (MSEL) assessed child development at 12 months. Associations between 5-HT levels and birth outcomes or developmental outcomes were assessed using linear regression models. Results No significant association was found between cord blood (n = 418) and placental (n = 89) 5-HT levels. Preterm birth was associated with lower cord blood 5-HT levels, and increasing gestational age among full-term infants was associated with higher cord blood 5-HT levels. Cord blood 5-HT was significantly associated with the Mullen Composite Score, and follow-up analyses revealed a significant association between cord blood 5-HT and fine motor skills. No association was found between placental 5-HT and the Mullen Composite Score. Conclusion To our knowledge, this study is the first to evaluate the relationship between placenta 5-HT levels and cord blood 5-HT levels at birth. The lack of association suggests that cord blood 5-HT levels are likely to be a better index of fetal 5-HT exposure. Associations between cord blood 5-HT and child cognitive development are consistent with previous studies showing an association between maternal 5-HT levels and neurodevelopmental trajectories. Further research is needed to better characterize these relationships and to elucidate the distinct contributions of maternal, placental, and fetal 5-HT sources across developmental time points.