A 24-year-old woman has a 28-day cycle. Progesterone levels are undetectable throughout the cycle. The most likely consequence and the mechanism of anovulation in this scenario are:

• A Anovulation is unlikely; progesterone is unnecessary for ovulation
• B Progesterone deficiency reduces LH surge amplitude, preventing follicle rupture
• C Anovulation is confirmed; progesterone is produced exclusively by the corpus luteum, which only forms after ovulation; absence of progesterone throughout the cycle indicates no corpus luteum formed, confirming anovulation ✓
• D Undetectable progesterone indicates luteal phase defect only; ovulation may have occurred

Explanation

Progesterone during the menstrual cycle is produced almost exclusively by the corpus luteum (CL), which forms only after ovulation from the luteinized granulosa and theca cells of the ruptured follicle under the influence of the post-ovulatory LH surge. Progesterone levels in the follicular phase are very low (<1 ng/mL, from adrenal). Progesterone rises sharply post-ovulation (days 18–22, levels >10 ng/mL confirm ovulation) and falls if no conception occurs (CL regression). Undetectable progesterone throughout the entire cycle—including the luteal phase (days 15–28)—confirms absence of corpus luteum formation, i.e., anovulation. This is used clinically as a mid-luteal progesterone level (day 21 in a 28-day cycle) to confirm ovulation: <3 ng/mL strongly suggests anovulation.

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

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Written and medically reviewed by the StethoPrep medical team.