The levonorgestrel-releasing intrauterine system (Mirena LNG-IUS, 52 mg) primarily prevents pregnancy by which mechanism?

• A Thickening of cervical mucus and endometrial decidualisation/atrophy impairing implantation and sperm penetration ✓
• B Suppression of ovulation in all users through consistent inhibition of the LH surge
• C Creation of a copper-ion toxic intrauterine environment that is spermicidal
• D Inhibition of sperm capacitation by progestogen-mediated fallopian tube ciliary arrest

Explanation

The LNG-IUS primarily acts locally: it releases 20 μg/day of levonorgestrel, causing profound endometrial atrophy/decidualisation (preventing implantation) and thick, hostile cervical mucus that impedes sperm penetration. Ovulation is suppressed in only 15–25% of cycles in the first year, declining further with time. The copper-IUD (not LNG-IUS) acts via copper ions. Tubal ciliary effects are minor and not the primary mechanism.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.