American Journal of Epidemiology Advance Access originally published online on September 4, 2007
American Journal of Epidemiology 2007 166(11):1306-1311; doi:10.1093/aje/kwm221
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ORIGINAL CONTRIBUTIONS |
Obesity and Oral Contraceptive Failure: Findings from the 2002 National Survey of Family Growth
From the Department of Public Health Sciences, The University of North Carolina at Charlotte, Charlotte, NC
Correspondence to Dr. Larissa R. Brunner Huber, The University of North Carolina at Charlotte, Department of Public Health Sciences, 9201 University City Boulevard, Charlotte, NC 28223-0001 (e-mail: lrhuber{at}uncc.edu).
Received for publication December 16, 2006. Accepted for publication June 29, 2007.
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 
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.
contraceptives; oral; obesity; women's health
Abbreviations: BMI, body mass index; CI, confidence interval; HR, hazard ratio; NSFG, National Survey of Family Growth; OR, odds ratio
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