## Why option 1 is right The LH surge at mid-cycle (Day 14) is uniquely triggered by **positive feedback** from sustained high estradiol (>200 pg/mL for >50 hours), a switch from the negative feedback that dominates the follicular phase. This surge causes **resumption of meiosis I** in the oocyte (which has been arrested in prophase since fetal life) and **extrusion of the first polar body**—the immediate meiotic consequence. Ovulation (follicular rupture) follows ~36 hours after the LH surge peak. This is the pathophysiological basis of ovulation predictor kits, which detect urine LH to identify peak fertility (day of surge + 2 days). [Williams Obstetrics 26e; Guyton & Hall 14e Ch 82] ## Why each distractor is wrong - **Option 2**: Progesterone drops in the luteal phase *after* ovulation and corpus luteum formation; it does not trigger the LH surge. The LH surge occurs *before* significant progesterone rise and is driven by estradiol positive feedback, not progesterone withdrawal. - **Option 3**: FSH is suppressed *after* the LH surge due to rising inhibin and progesterone; it does not sustain the surge itself. Ovulation occurs at Day 14, not Day 21. Low-level FSH would not trigger the surge—high estradiol does. - **Option 4**: Inhibin B is a product of the corpus luteum (luteal phase), not the pre-ovulatory follicle. Inhibin B does not trigger the LH surge; it suppresses FSH in the luteal phase. Luteinization occurs *after* the LH surge, not before, and requires the surge to occur. **High-Yield:** The LH surge is the *only* point in the menstrual cycle where estradiol exerts positive (not negative) feedback—this switch is essential for ovulation and is the target of ovulation predictor kits. [cite: Williams Obstetrics 26e; Guyton & Hall 14e Ch 82]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.