title: Obesity and oral contraceptive failure: findings from the 2002 National Survey of Family Growth.
abstract: Oral contraceptives are the most popular reversible method of contraception in the United States. Although most women using oral contraceptives are reliably protected against pregnancy, nearly half of the 3 million unintended pregnancies in the United States annually occur among the 90% of women who use contraception. Recent findings suggest that obesity may reduce the biologic effectiveness of oral contraceptives. The purpose of this study was to further investigate the potential obesity-oral contraceptive failure association using 2002 National Survey of Family Growth data. In this retrospective cohort of 1,491 women, body mass index (kg/m2) was derived from self-reported values, and oral contraceptive failure was defined as conceptions that occurred while women used oral contraceptives. Hazard ratios and 95% confidence intervals were obtained from Cox proportional hazards models. Obese women (body mass index > or = 30 vs. 18.5-24.9) had an increased risk of oral contraceptive failure (hazard ratio = 1.59, 95% confidence interval: 0.94, 2.68). Results were largely attenuated after adjustment for age, race/ethnicity, and parity. This population-based study found no association between obesity and oral contraceptive failure. While it is possible that misclassification or uncontrolled confounding obscured a true relation, it may be that there is no association. Large, prospective studies are needed to assess whether obesity plays a biologically relevant role in oral contraceptive effectiveness.
authors.affiliation: Department of Public Health Sciences, The University of North Carolina at Charlotte, Charlotte, NC 28223-0001, USA. lrhuber@uncc.edu
authors.forename: Larissa R
authors.initials: LR
authors.lastname: Brunner Huber
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Toth
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D003276:Contraceptives, Oral / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006306:Health Surveys; D006801:Humans; D009765:Obesity / Q000150:complications* / Q000453:epidemiology; D011247:Pregnancy; D049168:Pregnancy, Unplanned; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D018570:Risk Assessment; D017211:Treatment Failure; D014481:United States