## Contraceptive Efficacy — Pearl Index and Failure Rates **Key Point:** The Pearl Index is the gold standard measure of contraceptive efficacy, expressed as the number of unintended pregnancies per 100 woman-years of use. ### Failure Rates by Method (Perfect Use) | Contraceptive Method | Pearl Index (Failures/100 woman-years) | Category | |---|---|---| | Copper IUD (Cu-T 380A) | 0.6–0.8 | **Lowest reversible** | | Levonorgestrel IUD | 0.2–0.4 | Lower | | Implant (3-year) | 0.05 | Lowest overall | | Combined OCP | 0.3–0.5 | Low | | Barrier methods | 2–3 | Moderate | | LAM | 2–5 | Moderate | | Spermicide alone | 3–4 | Moderate | **High-Yield:** Among **reversible** methods (excluding permanent sterilization), the **copper IUD has the lowest failure rate** in perfect use, with a Pearl Index of 0.6–0.8 per 100 woman-years. This is superior to hormonal methods (OCP: 0.3–0.5) and significantly better than barrier methods (condom: 2–3). ### Why IUD Efficacy Is Superior 1. **No user-dependent factors** — once inserted, efficacy is not compromised by compliance, timing, or technique errors. 2. **Dual mechanism** — copper ions create a spermicidal environment and prevent implantation. 3. **Long-acting** — efficacy maintained for 10–12 years without reinitiation. **Clinical Pearl:** Although LAM (lactational amenorrhea method) and LAM-based methods are highly effective in the first 6 months postpartum (>99% with exclusive breastfeeding), they are **not** classified as a primary reversible contraceptive for general population counseling and have higher typical-use failure rates. **Mnemonic:** **IUDS** — **I**ntrauterine **D**evices are **S**uperior in efficacy (lowest Pearl Index among reversible methods). [cite:Park 26e Ch 9]
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