Cortisol levels in umbilical cord plasma in relation to labor and delivery.

Cortisol was determined by a competitive protein-binding method in umbilical cord plasma from pregnancies of 37 or more weeks' gestation. In 162 cases of vaginal delivery following spontaneous labor the mean +/- S.E. of cortisol values was 7.43 +/- 0.29 mug per 100 ml. of plasma. This cortisol level was not significantly different from that observed in 51 cases of vaginal delivery after oxytocin-induced labor (6.53 +/- 0.49 mug per 100 ml.) or in 47 cases of delivery by emergency cesarean section following labor (6.21 +/- 0.66 mug per 100 ml.). The mean cortisol level in cases of elective cesarean section with no prior labor (4.67 +/- 0.60 mug per 100 ml.) was significantly less than the value for vaginal delivery after spontaneous or induced labor. The cord plasma and amniotic fluid concentrations of cortisol in a pregnancy complicated by fetal anencephaly and terminated at 44 weeks by induction were normal. It is concluded that labor and vaginal delivery resulted in a significant increase in cord plasma cortisol levels but there was no significant difference between spontaneous and induced labors. These findings do not support the hypothesis that a surge in fetal cortisol production immediately precedes and initiates spontaneous labor in human pregnancy.