Progesterone fetal

All can virilise directly or via metabolites (except progesterone and dydrogesterone) and fetal virilis-ation to the point of sexual ambiguity has occurred with vigorous use during pregnancy (see also Contraception, p. 721). 

Near term, hCG and, subsequently, progesterone levels fall. —Fetal cortisol may cause the decline in progesterone. 

The placenta produces several protein and steroid hormones (Figure 54-1). The major protein hormones are CG and placental lactogen (PL). The steroids include progesterone, estradiol, estriol, and estrone. The placenta secretes most of its products into the maternal circulation only small amounts reach the fetal circulation. Close proximity of the maternal blood vessels to the site of placental hormone production may explain some of this preferential accumulation of hormones in the maternal blood circulation. Generally, hormone production by the placenta increases in proportion to the increase in placental mass. Therefore concentrations of hormones derived from the placenta, such as PL, increase in maternal peripheral blood as the placenta increases in size CG, which peaks at the end of the first trimester, is an exception. 

Zander (Z2) has shown by both in vitro and in vivo experiments that much of the 20a-dihydroprogesterone produced by the fetus from placental progesterone may be reconverted to progesterone by the placenta, and thus a placental-fetal circulation is possible of some of the progesterone produced by the placenta. 

The high concentration of progesterone in fetal blood may be responsible for the low activity of 3yS-HSD in the fetus and in the infant. Progesterone occupies a key position in the normal chain of steroid synthesis (Fig. 8), and it might be expected from the known effects of increases in product concentration upon the activities of other enzymes that inhibition... 

It has been shown that the fetal adrenal can convert progesterone and pregnenolone into cortisol in substantial yield (Sections 4.2.1 and 4.2.2), and, notably, Solomon (S25), after perfusion of fetuses with proges-terone-4- C, has isolated radioactive corticosterone and cortisol from the... 

In the fetus, the adrenal glands grow fast, are of large size, and are extremely active. They also use the large amounts of progesterone supplied by the placenta to synthesize cortisol, but most of the cortisol present in fetal blood is apparently from the mother s blood—at least in experiments using nonhuman primates.44... 

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