[Endocrino-pharmacological study of reproduction: Role and biosynthesis of steroid hormones in the feto-placental unit].

Although considerable information is available concerning steroidogenesis in the human fetus, the function of the different steroids formed during pregnancy and the factors regulating this delicate hormones balance are poorly understood. During human pregnancy, the placenta synthesizes large quantities of progesterone, estradiol, estrone and estriol and secretes these hormones into both the maternal and fetal circulations; progesterone from maternal lipoprotein-cholesterol, estradiol and estrone from maternal and fetal dehydroepiandrosterone sulfate (DHAS), and estriol largely from fetal 16 alpha-OH-DHAS. It has been demonstrated that preimplantation blastocysts of several animal species have the capacity to accumulate steroids to pregnenolone to progesterone, and to interconvert estrone and estradiol. Estetrol (E4), 15 alpha-hydroxy derivative of estriol is an interesting compound, since its formation is relatively unique to fetal liver function. Of special interest is that placental sulfatase deficiencies result in an extension of the gestation, and Cesarean section has to be done. This raises the question of the role of estrogens in determining the onset of labor, much as in the case of anencephaly. In general, progesterone may decline prior to an abortion, but there has not been a direct application to clinical practice. Estrogen levels during pregnancy are influenced by factors other than fetal well-being and include fetal weight, placental enzyme function, fetal adrenal function, maternal intestinal flora, maternal renal excretion and maternal liver function. Although not yet extensively utilized, such a dynamic test as the infusion of DHAS may yield useful information within a short period in otherwise complicated cases related to fetal and placental function.