Placental concentrations of progesterone, estradiol-17 beta, and cyclic AMP at delivery.

In contrast to most mammals, human parturition is not preceded by a rise in the estradiol : progesterone ratio in peripheral plasma. Thus tissue concentrations of progesterone, estradiol-17 beta, and cyclic adenosine monophosphate (AMP) were measured in placentas obtained after spontaneous vaginal delivery (SVD, N = 11), after oxytocin-induced labor (OXIL, N = 5), and at elective cesarean section (ECS, N = 8). Both progesterone and estradiol were higher in placentas obtained from SVD compared with those from ECS (progesterone: 2.95 +/- 0.26 versus 1.96 +/- 0.29 ng/mg tissue, P < .025; estradiol: 33.6 +/- 5.2 versus 26.4 +/- 3.8 pg/mg). Placentas from OXIL had intermediate progesterone (2.50 +/- 0.47 ng/mg) but the highest estradiol concentration (41.4 +/- 3.2 pg/mg). Cyclic AMP was 29.8 +/- 1.5, 39.6 +/- 8.0, and 35.9 +/- 3.9 pmoles/100 mg tissue in SVD, OXIL, and ECS placentas, respectively. Thus no rise in the placental estradiol : progesterone ratio was found in association with spontaneous labor.