Productivity of estrogens by human placental organ culture at different stages of gestation.

The productivity of estrogens from 6 to 39 weeks of pregnancy was assessed by using human placental organ culture. It was revealed that the placenta gains the capacity to generate a significant amount of estrogens at around 8 weeks of pregnancy. Therefore, it was suggested that the luteoplacental shift takes place between 6 and 8 weeks of gestation (or 4 to 6 weeks after fertilization). The productivity of estrogens showed a distinct difference before and after 10 weeks of pregnancy when the placental localization is established. The amount of estrone formed by the placenta before 10 weeks of pregnancy was 0.043 +/- 0.005 nanomoles/mg protein/hour (mean +/- s.e, n = 6), while it was 0.034 +/- 0.002 nanomoles/mg protein/hour from 10 weeks to term (mean +/- s.e, n = 18 ; not significantly different) during which no marked change was observed, however that of 17 beta-estradiol was 0.099 +/- 0.002 nanomoles/mg protein/hour (mean +/- s.e, n = 6) before 10 weeks of pregnancy and 0.072 +/- 0.002 nanomoles/mg protein/hour (mean +/- s.e, n = 18) from 10 weeks to term (significant difference with p less than 0.005). The 17 beta-estradiol/estrone ratio remained almost constant throughout pregnancy, which ranged from 2.00 to 3.00.