Subcutaneous etonogestrel implant (Nexplanon) prevents pregnancy primarily through which mechanism?
- A Endometrial atrophy preventing implantation
- B Inhibition of ovulation via suppression of LH surge ✓
- C Increased endometrial prostaglandin production causing luteal phase defect
- D Thickening of cervical mucus as the sole mechanism
Correct answer: B. Inhibition of ovulation via suppression of LH surge
Explanation
Etonogestrel (the active metabolite of desogestrel) implant prevents pregnancy predominantly by inhibiting the LH surge and hence ovulation. At therapeutic serum concentrations, ovulation suppression is consistent and nearly complete (~96–99% of cycles). Secondary mechanisms include cervical mucus thickening (reducing sperm penetration) and endometrial atrophy. The primary mechanism is ovulation inhibition, not just endometrial or cervical effects. Its three-year failure rate is approximately 0.05%, making it the most effective reversible contraceptive.
Reference: Shaw's Textbook of Gynaecology, 17th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.