A 35-year-old woman on a progestin-only pill (desogestrel 75 mcg) develops breakthrough bleeding. The mechanism of action of desogestrel POP that differs MOST from levonorgestrel POP (traditional dose) is:

• A Desogestrel consistently suppresses ovulation in >97% of cycles; LNG-POP relies primarily on cervical mucus thickening ✓
• B Desogestrel selectively binds androgen receptors to suppress LH surge; LNG-POP has no anti-androgenic activity
• C Desogestrel has zero progestogenic activity and works solely by endometrial effects
• D Desogestrel inhibits tubal motility via progesterone receptors in fallopian tube musculature; LNG relies on implantation failure

Explanation

Desogestrel 75 mcg daily (Cerazette, Slinda) is a 'continuous progestogen-only pill' that consistently suppresses ovulation in >97% of cycles due to its higher progestogenic potency and sustained receptor activity — making it more effective than traditional levonorgestrel POPs (which were studied at doses that did not reliably suppress ovulation in 40–60% of cycles). LNG-POP's primary contraceptive mechanisms are cervical mucus thickening (making it hostile to sperm) and endometrial changes, with ovulation suppression inconsistent. This is the key pharmacological distinction explaining why desogestrel POP approaches combined pill efficacy (Pearl Index <1) while traditional POPs have higher failure rates with delayed or missed doses. Option B is incorrect — desogestrel's androgenic receptor activity is low, not the mechanism of action difference described.

Reference: Shaw's Textbook of Gynaecology, 17th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.