Steroid concentrations and delta 5, 3 beta-hydroxysteroid dehydrogenase activity in human placenta. Comparison between elective cesarean section and spontaneous vaginal delivery.

The level of delta 5, 3 beta-hydroxysteroid dehydrogenase (delta 5, 3 beta-HSDH) was measured in the mitochondrial and microsomal fractions of the human term placenta. The capability of the placenta to transform pregnenolone to progesterone was found to be significantly higher after spontaneous vaginal delivery than after elective cesarean section (p < 0.001). There was a significant rise in the placental concentration of estrone occurring at the time of parturition (p < 0.01). The placental concentration of estradiol-17 beta was also greater after than before parturition but the diffference was not statistically significant. Conversely to the estrogen concentration, no difference existed in the progesterone concentration between the two groups of placentas. The significance of these findings is discussed in relation to the parturition process.