The Human Fetus Preferentially Secretes Corticosterone, Rather than Cortisol, in Response to Intra-Partum

Context: Fetal stress is relevant to newborn outcomes. Corticosterone is rarely quantified in human clinical endocrinology and is found at much lower concentrations than cortisol. However, fetal corticosterone is a candidate hormone as a fetal stress signal. Objective: Test the hypothesis that preferential fetal corticosterone synthesis occurs in response to fetal intra-partum stress. Design: Cross-sectional comparison of paired serum corticosteroid concentrations in umbilical artery and vein from 300 women providing consent at admission to a General Hospital Labor and Delivery unit. Pre-term and multiple births were excluded, leaving 265 healthy deliveries. Main Outcome Measures: Corticosterone and cortisol concentrations determined by LC-MS/MS for umbilical cord venous (V) and arterial (A) samples and used to calculate fetal synthesis (A2V) and proportional fetal synthesis ([A2V]/V). Chart-derived criteria stratified samples by type of delivery, maternal regional analgesia, augmentation of contractions, and clinical rationale for emergent Caesarian delivery. Results: Cortisol concentrations were higher than corticosterone concentrations; however, the fetus preferentially secretes corticosterone (148 % vs 49 % proportional increase for cortisol) and differentially secretes corticosterone as fetal stress increases. Fetal corticosterone synthesis is elevated after passage through the birth canal relative to Caesarian deliveries. Fo