A 26-year-old woman is on combined oral contraceptives. Which of the following mechanisms MOST specifically suppresses ovulation?
- A Continuous progestin exposure suppresses GnRH pulsatility from the hypothalamus, reducing LH pulse frequency and preventing the mid-cycle LH surge that triggers ovulation ✓
- B Estrogen component directly inhibits FSH-stimulated follicular development by binding FSH receptors on granulosa cells
- C Progestin thickens cervical mucus, physically preventing sperm from reaching the egg even if ovulation occurs
- D Ethinylestradiol elevates SHBG, reducing free testosterone, which is required for normal folliculogenesis
Explanation
The primary mechanism of ovulation suppression by combined OCP is the progestin component suppressing GnRH pulsatility at the hypothalamus. GnRH must be secreted in a specific pulsatile pattern (approximately 90-minute intervals) to maintain appropriate LH and FSH secretion. Continuous progestogen exposure suppresses GnRH pulse frequency, which reduces LH pulsatility and prevents the estrogen-positive feedback-induced mid-cycle LH surge that triggers ovulation. The estrogen component (option B) contributes by suppressing FSH (negative feedback), limiting follicular development, and provides cycle control — but the LH surge suppression by progestin is the key ovulation-inhibiting mechanism. Cervical mucus thickening (option C) is a secondary contraceptive mechanism, not the primary anti-ovulatory one. Option D is a pharmacological effect but not the mechanism of ovulation suppression.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.