In a normal 28-day cycle with ovulation on day 14, on which day would you expect to measure elevated estradiol with low progesterone?

In a normal 28-day cycle with ovulation on day 14, on which day would you expect to measure elevated estradiol with low progesterone?

• A. Day 14
• B. Day 18
• C. Day 21
• D. Day 12

Answer: (D)

During the follicular phase, estradiol rises while progesterone remains low because the corpus luteum hasn’t formed yet. The preovulatory estrogen peak occurs about 1–2 days before ovulation, which in a 28-day cycle with ovulation on day 14 lands around day 12. After ovulation, the luteal phase begins and progesterone rises. So the combination of high estradiol with low progesterone is most consistent with day 12.

During the follicular phase, estradiol rises while progesterone remains low because the corpus luteum hasn’t formed yet. The preovulatory estrogen peak occurs about 1–2 days before ovulation, which in a 28-day cycle with ovulation on day 14 lands around day 12. After ovulation, the luteal phase begins and progesterone rises. So the combination of high estradiol with low progesterone is most consistent with day 12.