Which feature best distinguishes the contraceptive efficacy of copper intrauterine devices (Cu-IUD) from levonorgestrel intrauterine systems (LNG-IUS) in typical use among Indian women?

Explanation

## Mechanism of Contraceptive Action: Cu-IUD vs LNG-IUS ### Copper IUD (Cu-IUD) - **Primary mechanism:** Local endometrial toxicity and foreign body reaction - Creates a hostile intrauterine environment - Does NOT suppress ovulation - Sperm motility and viability reduced by copper ions - Pearl index: 0.8 per 100 woman-years (excellent efficacy) ### Levonorgestrel IUS (LNG-IUS) - **Primary mechanism:** Systemic hormonal suppression + local endometrial atrophy - Releases levonorgestrel directly into uterine cavity - Suppresses ovulation in 20–40% of cycles (variable) - Thickens cervical mucus - Causes endometrial atrophy - Pearl index: 0.2 per 100 woman-years (superior efficacy) **Key Point:** The fundamental distinction is that LNG-IUS achieves contraception through **hormonal suppression** (ovulation + endometrial changes), while Cu-IUD achieves it through **non-hormonal local mechanisms** (endometrial toxicity and sperm immobilization). ### Comparison Table | Feature | Cu-IUD | LNG-IUS | | --- | --- | --- | | **Mechanism** | Local endometrial toxicity | Systemic + local hormonal | | **Ovulation suppression** | No | Yes (20–40% cycles) | | **Pearl index** | 0.8 per 100 WY | 0.2 per 100 WY | | **Duration** | 10 years | 5 years | | **Hormonal side effects** | None | Possible (mood, breast tenderness) | | **Menstrual bleeding** | Often increased | Often decreased | **High-Yield:** This distinction is crucial for counselling: choose Cu-IUD if hormonal contraception is contraindicated; choose LNG-IUS if menorrhagia is a concurrent problem (therapeutic benefit). **Clinical Pearl:** Both are tier-1 reversible contraceptives with >99% efficacy in perfect use. The choice depends on patient preference, side effect profile, and concurrent gynecological conditions. [cite:Park 26e Ch 8]