Steroid concentrations in human myometrial and placental tissues at week 39 of pregnancy.

Endogenous levels of P, E1, and E2 were determined by radioimmunoassay in human myometrium and placenta at week 39 of pregnancy. In the myometrium, P and estrogens were higher in the inner layer near the placenta than in other zones. Higher E2/P ratios were found in placental sites. A large difference in the E2/P ratios was observed between placenta and corresponding adjacent myometrial area, indicating an easier diffusion of E2 from the site of its production.