Plasma acth levels in the human fetus and neonate as related to age and parturition

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.