CORD SERUM PROLACTIN IN RELATION TO THE TIME OF THE DAY, THE SEX OF THE NEONATE AND THE BIRTH WEIGHT

Abstract

Serum prolactin was measured in 581 blood samples collected immediately after birth from 563 single new-born and from 9 pairs of twins. Cord serum prolactin is high at birth: the mean level is some 5 times higher than in adults. There is no sex difference in cord serum prolactin concentration in the neonate. Mean serum prolactin is significantly higher at 1.00 and 2.00 a.m. Thus a circadian periodicity in serum prolactin concentration seems to appear already during foetal life well before the organization of sleep rhythm. Cord serum prolactin increases with birth weight ranging from 1500 g to 3500 g. Thus, the control of levels of circulating prolactin changes during foetal life resulting in a progressive increase starting from mid-pregnancy. Mean cord serum prolactin at birth is lower in twins than in single new-borns. There is no significant difference in serum prolactin between the first and the second twin.