Prolactin levels were measured by radioimmunoassay in umbilical cord plasma from fetuses, in capillary plasma from neonates, and in venous plasma from adults. The concentrations of prolactin in cord plasma from fetuses having gestational ages of 16 to 19 weeks, 20 to 34 weeks, and 35 to 42 weeks were 53 +/- 16 (mean and SE), 233 +/- 30 and 371 +/- 7 ng/ml, respectively. The prolactin levels decreased to 218 +/- 35 ng/ml during the first neonatal week. The similarity of the patterns of prolactin levels, reported gestational estrogen levels and adrenal weights, as well as the known biological properties of prolactin, estrogen, and ACTH is consistent with the view that these three factors may be involved in the growth of the fetal adrenal cortex and its involution in the newborn.

ACTH levels were measured by radioimmunoassay in umbilical cord plasma from fetuses, in capillary plasma from neonates, and in venous plasma from adults. Cord plasma was obtained from term fetuses delivered under the following four conditions: 1) vaginally after spontaneous labor, 2) by cesarean section after spontaneous labor, 3) by cesarean section before spontaneous labor, and 4) vaginally after oxytocin-induced labor.The ACTH values in these four groups of term fetuses did not differ significantly. Thus, human umbilical cord ACTH does not rise with spontaneous labor. The concentration of ACTH in cord plasma prior to the 34th gestational week was 241 ± 33 pg/ml (mean and SE); and in term fetuses, the ACTH levels were 143 ± 7 pg/ml. In infants during the first week of life, the ACTH concentration was 120 ± 8 pg/ml. The mean ACTH level in all fetuses was higher than the afternoon values in normal adults (43 ± 4 pg/ml). These results suggest that an increased ACTH concentration in fetal plasma is not essential for the initiation of labor in the human. (/ Clin Endocrinol Metab 39: 269,1974)