Body weight and risk of oral contraceptive failure

Obstet Gynecol. 2002 May;99(5 Pt 1):820-7. doi: 10.1016/s0029-7844(02)01939-7.


Objective: To examine the hypothesis that higher body weight increases the risk of oral contraceptive (OC) failure.

Methods: We conducted a retrospective cohort analysis of data from 755 randomly selected female enrollees of Group Health Cooperative of Puget Sound who completed an in-person interview and dietary questionnaire between 1990 and 1994 as control subjects for a case-control study of ovarian cysts. Among the 618 women who were OC ever-users, we used Cox proportional hazards regression models to estimate the relative risk (RR) of pregnancy while using OCs associated with body weight quartile.

Results: During 2822 person-years of OC use, 106 confirmed pregnancies occurred (3.8 per 100 person-years of exposure). After controlling for parity, women in the highest body weight quartile (70.5 kg or more) had a significantly increased risk of OC failure (RR 1.6, 95% confidence interval [CI] 1.1, 2.4) compared with women of lower weight. Higher elevations of risk associated with the highest weight quartile were seen among very low-dose OC users (RR 4.5, 95% CI 1.4, 14.4) and low-dose OC users (RR 2.6, 95% CI 1.2, 5.9), controlling for parity, race, religion, and menstrual cycle regularity.

Conclusion: Our findings suggest that body habitus may affect metabolism sufficiently to compromise contraceptive effectiveness. Consideration of a woman's weight may be an important element of OC prescription.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Absorption
  • Adipose Tissue / metabolism
  • Adolescent
  • Adult
  • Body Mass Index
  • Body Weight*
  • Cohort Studies
  • Contraception*
  • Contraceptives, Oral* / pharmacokinetics
  • Female
  • Humans
  • Interviews as Topic
  • Pregnancy
  • Proportional Hazards Models
  • Retrospective Studies
  • Risk Factors
  • Surveys and Questionnaires


  • Contraceptives, Oral