The Pearl Index for combined oral contraceptive pills is approximately 0.3 with perfect use and 7–9 with typical use. The Pearl Index is defined as:

• A Probability of pregnancy in the first month of contraceptive use
• B Number of contraceptive failures per 1000 woman-months of use
• C Percentage of couples achieving contraceptive success at 12 months
• D Number of pregnancies per 100 women per year of contraceptive use ✓

Explanation

The Pearl Index (failure rate) = (number of unintended pregnancies / total months of exposure) × 1200. It expresses contraceptive failure as the number of pregnancies per 100 woman-years of exposure. A lower Pearl Index indicates higher contraceptive efficacy. The index assumes a constant failure rate over time, which may not hold for all methods.

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

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Written and medically reviewed by the StethoPrep medical team.