The 'Pearl Index' of a contraceptive method is calculated as the number of unintended pregnancies per 100 woman-years of use. A method with a Pearl Index of 0.1 means:

• A 1 in 10 women using the method for 1 year will become pregnant
• B 1 pregnancy per 1,000 woman-years of use ✓
• C 0.1% of women become pregnant per month of use
• D 10 unintended pregnancies per 100,000 woman-years

Explanation

Pearl Index = (number of unintended pregnancies / total months of exposure) × 1200 = pregnancies per 100 woman-years. A Pearl Index of 0.1 means 0.1 pregnancies per 100 woman-years = 1 pregnancy per 1,000 woman-years. This represents very high contraceptive efficacy (e.g., LARC methods like implants and IUDs achieve Pearl Index <0.1). Combined OCPs have a Pearl Index of ~0.3 (perfect use) to ~8 (typical use). Barrier methods (male condom) have a Pearl Index of ~2 (perfect use) to 15 (typical use).

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.