PHASIC MATERNAL PROLACTIN SECRETION DURING SPONTANEOUS LABOR IS ASSOCIATED WITH CERVICAL DILATATION AND 2ND-STAGE UTERINE ACTIVITY

OBJECTIVE: In this study, we attempted to determine the physiologic roles of prolactin (PRL) and hCG during labor. METHODS: Serial blood samples were collected from 19 women (15 multiparous and four nulliparous) before, during, and after labor; assayed for PRL and hCG; and compared with cervical dilatation and uterine contraction frequency. RESULTS: Prolactin levels decreased in association with progressive cervical dilatation during the first stage of labor and reached a nadir at full dilatation. Thereafter, PRL increased rapidly during the second stage of labor and peaked within 1 hour postpartum. Uterine contraction frequency also increased during the second stage and correlated significantly (r(2) = 0.60; P = .0006) with levels of PRL. Levels of hCG increased during labor and peaked at about the time of delivery. CONCLUSION: These data suggest that phasic PRL secretion is associated with cervical dilatation and that after transition to the second stage of labor, uterine contraction frequency may be associated with the increase in PRL levels.