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About 75 million women worldwide use combined oral contraceptives (OCs) to prevent pregnancy. In a secondary analysis of data from an industry-supported study, researchers assessed OC effectiveness, as well as factors that might influence effectiveness. For as long as 5 years, the investigators followed 59,000 women (mean baseline age, 25; mean baseline BMI, 22 kg/m2) from seven European countries who received OC prescriptions (first-time or switching to new OCs). Only 1400 women were lost to follow-up. Data were self-reported at baseline and every 6 months; study physicians verified unplanned pregnancies and determined their causes by interview.
During 112,659 woman-years of OC use, 545 unplanned pregnancies were reported (0.5 pregnancies p…