What compound is the precursor to placental estriol?

The correct precursor to placental estriol is adrenal C19 steroids. Estriol, a hormone produced primarily during pregnancy, is synthesized from the androgens derived from both the fetus and the placenta.

In the placental context, the synthesis of estriol involves the conversion of dehydroepiandrosterone sulfate (DHEAS), which is an adrenal C19 steroid produced by the fetal adrenal glands. The placenta then converts DHEAS into estriol through a series of enzymatic reactions.

In contrast, while testosterone might play a role in the synthesis of other estrogens or androgens, it is not a direct precursor to estriol in the same pathway. Estrone, another estrogen, is also not the direct precursor since it is derived from other sources and contributes to a different pathway of estrogen synthesis. Similarly, 17-hyroxyprogesterone (17-OHP) is primarily involved in the steroidogenesis leading to glucocorticoids and mineralocorticoids rather than playing a direct role in the synthesis of estriol.

Understanding this pathway and the roles of different steroids is crucial for comprehending hormonal changes during pregnancy and their physiological implications.