Adrenocorticotropic hormone in human fetal blood at delivery.

Adrenocorticotropic hormone (ACTH) concentrations in umbilical arterial and venous plasma were measured in newborn infants delivered both vaginally and by cesarean section. Mean ACTH was significantly higher in the arterial (602.0 pg. per milliliter) than venous (261.5 pg. per milliliter) plasma in vaginal deliveries (pless than 0.01). Arterial plasma of babies born by elective cesarean section before initiation of labor contained less ACTH (384.7 pg. per milliliter) when compared to those delivered after labor had started (698.7 pg. per milliliter). Serial determinations of ACTH in pooled fetal blood obtained during labor showed that the average hormone titers increased significantly from first stage (295.2 pg. per milliliter) to second stage of labor (440.5 pg. per milliliter), and reached a peak at delivery (645.4 pg. per milliliter). The pituitary gland of the fetus at midtrimester contained ACTH. Possible mechanisms for fetal secretion of ACTH at delivery are discussed.