Which mechanism distinguishes the levonorgestrel-releasing intrauterine system (LNG-IUS, Mirena) from the copper IUD as a contraceptive?

• A LNG-IUS primarily acts by preventing fertilization via copper ion toxicity
• B LNG-IUS causes endometrial atrophy and thickens cervical mucus, primarily preventing implantation and sperm penetration ✓
• C LNG-IUS is equally effective in all uterine positions unlike the copper IUD
• D LNG-IUS has no systemic hormonal effects

Explanation

LNG-IUS (Mirena) releases levonorgestrel locally, producing endometrial atrophy (glandular suppression and stromal decidualization), marked thickening of cervical mucus impairing sperm penetration, and some ovulatory suppression in early cycles. These mechanisms prevent fertilization and implantation. Copper IUD acts through copper ion spermicidal toxicity and inflammatory endometrial reaction. LNG-IUS does have measurable systemic progestogen effects (acne, mood changes in some users).

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.