Human chorionic gonadotropin (hCG) is produced by the syncytiotrophoblast from the day of implantation. Its primary physiologic role in early pregnancy is:

• A To directly stimulate uterine myometrial quiescence via oxytocin receptor downregulation
• B To rescue the corpus luteum from luteolysis by binding LH receptors, sustaining progesterone production until the placenta can take over steroidogenesis (luteo-placental shift, ~8–10 weeks) ✓
• C To suppress maternal immune response by blocking NK cell cytotoxicity in the decidua
• D To stimulate fetal adrenal androgen production for fetoplacental estrogen synthesis from the beginning of implantation

Explanation

Without hCG rescue, the corpus luteum would involute ~10–14 days after ovulation (luteolysis), withdrawing the progesterone support needed to maintain the decidualized endometrium. hCG, which is structurally homologous to LH and shares its receptor, sustains luteal progesterone production. As placental trophoblasts develop the capacity for de novo steroidogenesis by 8–10 weeks, the luteo-placental shift occurs and the corpus luteum is no longer required.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.