## Pearl Index and Contraceptive Efficacy The **Pearl Index** (also called Pearl Rate) measures contraceptive failure as the number of unintended pregnancies per 100 woman-years of use. Lower values indicate higher efficacy. ### Pearl Index Values for Common Reversible Methods | Contraceptive Method | Pearl Index (failures/100 woman-years) | Typical Use Failure Rate (%) | | --- | --- | --- | | LNG-IUS (Mirena) | 0.1–0.2 | 0.2 | | Cu-IUD (TCu380A) | 0.6–0.8 | 0.8 | | Combined oral pill | 3–8 | 9 | | Progestin-only pill | 2–3 | 9 | | Barrier methods | 10–15 | 18 | **Key Point:** The **LNG-IUS (levonorgestrel intrauterine system)** has the lowest Pearl Index among reversible contraceptives, making it one of the most effective reversible methods available. ### Why LNG-IUS is Superior 1. **Long-acting reversible contraception (LARC)** — no user-dependent factors 2. **Dual mechanism:** local progestin effect + foreign body reaction 3. **Thickened cervical mucus** + endometrial atrophy 4. **>99% efficacy** over 5 years **High-Yield:** LNG-IUS Pearl Index ≈ 0.1–0.2, Cu-IUD ≈ 0.6–0.8, oral pills ≈ 3–8. This ranking is frequently tested in epidemiology sections. **Clinical Pearl:** Although Cu-IUD has a slightly higher Pearl Index than LNG-IUS, both are considered "tier-1" LARC methods and far superior to user-dependent methods in real-world practice.
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