Regarding the levonorgestrel intrauterine system (LNG-IUS, Mirena), which statement about its mechanism of action is MOST accurate?

• A Acts primarily by inhibiting ovulation in all users
• B Acts primarily as a foreign body causing local inflammatory response
• C Acts primarily through local progestogenic effects causing endometrial suppression and cervical mucus thickening ✓
• D Acts by inhibiting tubal ciliary function preventing ovum transport

Explanation

The LNG-IUS releases 20 µg/day of levonorgestrel locally, with its primary contraceptive mechanism being endometrial decidualisation/atrophy and thickening of cervical mucus, which prevents sperm penetration. Ovulation is suppressed in approximately 25–30% of users but NOT consistently in all. This is distinct from systemic progestogen-only pills or implants. The local hormonal action rather than a foreign-body effect is the dominant mechanism.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.