Maternal prolactin secretion is phasic during induced term and post-term labor.

OBJECTIVE: We hypothesized that regimens of labor induction do not alter the biphasic secretion of maternal prolactin (PRL) seen during spontaneous labor.

METHODS: Serial blood samples drawn from 12 women before, during, and after induced labor were assayed for PRL and hCG and compared with cervical dilatation and uterine contraction frequency (UCF). Induction methods were cervical ripening with dinoprostone gel (Prepidil) followed by oxytocin infusion (n = 1), amniotomy followed by oxytocin (n = 4), oxytocin followed by amniotomy (n = 3), amniotomy only (n = 2), and oxytocin only (n = 2).

RESULTS: Regardless of the induction method, PRL decreased with advancing cervical dilatation during the first stage of labor and reached a nadir at full dilatation. Prolactin levels then increased rapidly during the second stage, correlating significantly with the increase in UCF, and peaked at 1 hour postpartum before decreasing. Levels of hCG increased during labor and peaked just before or at delivery before rapidly decreasing.

CONCLUSIONS: The biphasic secretion of maternal PRL is a fundamental characteristic of active term labor and occurs regardless of the method used to induce labor.