Oral contraceptive failures and body weight: Findings in a large cohort study

This report looks at data from 17 032 women who took part in tire Oxford Fa mily Planning Association contraceptive study. Thirty-eight first accidenta l pregnancies occurred during 6779 woman-years of use of progestogen-only o ral contraceptives (0.56 per 100) and 95 first accidental pregnancies occur red during 48 692 woman-years of combined oral contraceptive use (0.20 per 100). Although associations with age and parity were found, there was no ev idence of any influence of body weight on the risk of accidental pregnancy with either form of oral contraceptive.