In human pregnancy, amniotic fluid prolactin concentrations decline from peak values of 3000-4000 ng/ml at 19-25 wk of gestation to levels around 500 ng/ml between 35 and 41 wk. Kletzky et al. collected samples by transabdominal amniocentesis at 2-wk intervals and could discern no apparent decline at term. birth control pills
Kinoshita and coworkers compared prolactin levels in human amniotic fluid obtained at caesarean section before the onset of labor and by trans-vaginal amniocentesis during spontaneous labor with the cervix dilated. Prolactin concentrations before labor were approximately 3-fold higher than those during active labor, and they decreased with time as labor progressed. Maslar et al. obtained cross-sectional data from rhesus amniotic fluid collected at caesarean section before the onset of labor but not after 155 days of gestation (term is approximately 165 days). Despite similar peak concentrations, the pattern of prolactin accumulation in rhesus amniotic fluid differs somewhat from that in human pregnancy. After a progressive rise from 50 to 110 days of gestation, a plateau is reached and is maintained until term. We obtained samples by amniocentesis or by indwelling catheters in untreated monkeys at approximately 5-day intervals from 135 days of gestation until term and observed no significant decline in prolactin levels within 1-2 days of spontaneous delivery. Similarly, daily sampling in the baboon revealed no prepartum changes in amniotic fluid prolactin. Limited observations during labor, however, suggest that amniotic fluid prolactin declines after the onset of labor in the rhesus monkey.