What is the PRIMARY contraceptive mechanism of a correctly taken combined oral contraceptive pill?

• A Induction of endometrial atrophy sufficient to block implantation
• B Spermicidal effect on cervical mucus
• C Direct toxic effect on the blastocyst
• D Suppression of the midcycle LH surge, preventing ovulation ✓

Explanation

Oestrogen plus progestin suppresses GnRH pulsatility, abolishing the midcycle LH surge, so follicular rupture does not occur. Thickening of cervical mucus by the progestin component is a secondary mechanism, not a spermicidal action. Effects on the endometrium and tubal motility are ancillary. Because ovulation is the key event blocked, missed pills at the start of a pack carry the highest failure risk.

Reference: Williams Gynecology, 4th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.