Weight has little impact on OC efficacy

The effectiveness of oral contraception is unaffected by weight or body mass index (BMI), and failure rates decline with age and duration of use, according to a study of European users published in the September issue of the American Journal of Obstetrics and Gynecology.

Jürgen C. Dinger, MD, of the ZEG-Center for Epidemiology and Health Research in Berlin, and colleagues analyzed data from the European Active Surveillance Study on Oral Contraceptives on 59,510 users of oral contraception. The researchers looked at how effective the contraceptive method was overall and by a range of factors, including subjects' BMI, weight, age, dose, type of regimen, duration of use, and parity. They also confirmed by interview the 545 self-reported unplanned pregnancies.

The data covered 112,659 women-years of exposure to oral contraceptives (OCs) and revealed that weight and BMI had little impact on effectiveness, the investigators note. Women over the age of 30 years had lower rates of contraceptive failure, and increased duration of use was also associated with a drop in OC failure.

The study was funded by Bayer Schering Pharma AG.

Dinger JC, Cronin M, Möhner S, et al. Oral contraceptive effectiveness according to body mass index, weight, age, and other factors. Am J Obstet Gynecol. 2001: 263.e1-263.e9.