During pregnancy, a surge in placental hormones sustains the endometrium. Which mechanism explains why menstruation ceases despite the typical 28-day ovarian cycle's hormonal fluctuations?

💡 Explanation

Sustained progesterone from the placenta maintains the endometrium, preventing its breakdown and subsequent menstruation because this hormonal environment overrides the typical cyclic decrease in ovarian progesterone. Therefore, menstruation ceases, rather than continuing, due to endometrial maintenance, not vasoconstriction or corpus luteum failure.

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