Oral contraceptive effectiveness according to body mass index, weight, age, and other factors.

OBJECTIVE

The purpose of this study was to assess the use-effectiveness of oral contraceptives (OCs) in Europe according to body mass index (BMI), weight, age, and other factors.

STUDY

DESIGN

In a planned secondary analysis, we used data from the European Active Surveillance Study on Oral Contraceptives, which was a prospective active cohort surveillance study of 59,510 OC users, to assess the effectiveness of OCs overall and by BMI, weight, age, duration of use, ethinylestradiol dose, regimen type, starting/switching status, and parity. Self-reported unplanned pregnancies during OC use were confirmed by interview.

RESULTS

An analysis of OC effectiveness (112,659 women-years of exposure and 545 unplanned pregnancies) found little variation in effectiveness by BMI/weight. Failure rates decreased after 30 years of age and with an increasing duration of use.

CONCLUSION

OC users in Europe reported high contraceptive effectiveness with "typical use." Failure rates decreased with age and duration of use. BMI and weight had little, if any, influence on effectiveness.