The Pearl Index of a contraceptive method is the number of unwanted pregnancies per 100 woman-years of use. A contraceptive with a Pearl Index of 0.1 is best described as:
- A Moderately effective — 90% effective over one year of typical use
- B Requires backup contraception for full effectiveness
- C Highly effective — 99.9% effective over one year of typical use ✓
- D Equivalent to no contraception (typical user failure rate)
Correct answer: C. Highly effective — 99.9% effective over one year of typical use
Explanation
Pearl Index = (Number of failures / Total months of exposure) × 1200 (or × 1300 for woman-years). A Pearl Index of 0.1 means 0.1 pregnancies per 100 woman-years — i.e., only 1 pregnancy per 1000 women using the method for one year. This indicates 99.9% efficacy. The combined oral contraceptive pill has a Pearl Index of 0.1–0.3 with perfect use, while IUCD (Cu-T) has a Pearl Index of 0.6–0.8.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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Written and medically reviewed by the StethoPrep medical team.