Obesity Research Today is a free monthly online journal that collates and summarizes the latest research about Obesity, including details on health, diet, prevention, exercise.

Obesity and oral contraceptive failure: findings from the 2002 National Survey of Family Growth.

Brunner Huber LR, Toth JL

Department of Public Health Sciences, The University of North Carolina at Charlotte, Charlotte, NC 28223-0001, USA. lrhuber@uncc.edu

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.

Published 16 November 2007 in Am J Epidemiol, 166(11): 1306-11.
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