Which feature best distinguishes a copper-containing IUCD from a levonorgestrel-releasing IUCD (LNG-IUS) in terms of mechanism of contraceptive action?

Explanation

## Mechanism of Action: Copper vs. Hormonal IUCDs ### Copper IUCD (Cu-T, Multiload) **Key Point:** Copper IUCDs work primarily through **local spermicidal and spermostatic effects** in the uterine cavity. 1. Copper ions are released and create a hostile environment for sperm 2. Enhance local inflammatory response in endometrium 3. Impair sperm motility and viability 4. Prevent fertilization at the level of the fallopian tube 5. Do NOT prevent ovulation — ovulation occurs normally ### Levonorgestrel-Releasing IUS (LNG-IUS / Mirena) **Key Point:** LNG-IUS works through **both local and systemic mechanisms**. 1. **Local effects:** Thickens cervical mucus, alters endometrium, impairs sperm transport 2. **Systemic effects:** Low-dose progestin suppresses ovulation in ~20% of cycles (unlike copper) 3. Causes endometrial atrophy → amenorrhea or hypomenorrhea (therapeutic benefit) 4. Provides systemic contraceptive backup beyond the uterine cavity ### Comparative Table | Feature | Copper IUCD | LNG-IUS | | --- | --- | --- | | **Primary mechanism** | Spermicidal/local inflammation | Local + systemic progestin | | **Ovulation** | Occurs normally | Suppressed in ~20% cycles | | **Menstrual bleeding** | Heavy/prolonged (common) | Reduced/amenorrhea (therapeutic) | | **Systemic hormone** | None | Low-dose levonorgestrel | | **Endometrial effect** | Minimal atrophy | Marked atrophy | | **Duration** | 10 years (Cu-T 380A) | 5–7 years (Mirena) | **High-Yield:** The **spermicidal copper ion environment** is the single best discriminator — it is the defining local mechanism of copper IUCDs and is absent in hormonal devices. **Clinical Pearl:** Copper IUCDs are ideal for women who want to avoid systemic hormones but can tolerate heavier periods; LNG-IUS is preferred in women with menorrhagia or dysmenorrhea seeking therapeutic benefit.