Near term, the placenta produces large amounts of estriol. The obligatory precursor for placental estriol synthesis is supplied by which source?
- A Fetal adrenal cortex as dehydroepiandrosterone sulfate ✓
- B Maternal ovarian theca cells as dehydroepiandrosterone sulfate
- C Fetal liver as 16-hydroxylated cholesterol
- D Maternal liver conversion of placental progesterone
Correct answer: A. Fetal adrenal cortex as dehydroepiandrosterone sulfate
Explanation
The placenta lacks 17-alpha-hydroxylase and 17,20-lyase activity, so it cannot convert progesterone to androgens. It depends entirely on fetal adrenal DHEA sulfate, which undergoes 16-hydroxylation in the fetal liver before placental sulfatase and aromatase convert it to estriol. This fetal-placental unit means falling estriol levels signal fetal adrenal compromise, while maternal ovaries contribute little steroid after early pregnancy.
Reference: Williams Obstetrics, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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