The Role of Body Weight in Oral Contraceptive Failure: Results from the 1995 National Survey of Family Growth
Introduction
Each year, 3 million of the 6 million pregnancies in the US are classified as unintended (1). It is estimated that nearly half of these unintended pregnancies occur in the 90% of women who use some type of contraceptive (2). Researchers attribute these contraceptive failures to noncompliance and ineffective use 2, 3, 4, 5. Few studies have investigated whether biologic factors, rather than ineffective use, may be responsible for the large number of pregnancies that occur in women using contraceptives. Body weight is one such biologic factor that may affect how contraceptives work, specifically hormonal contraceptives. Excess weight may cause an enhanced metabolic rate and hence more rapid drug metabolism (6). Suggestions of the association between higher body weight and increased contraceptive failure emerge from secondary analyses of efficacy trials of Norplant and the transdermal contraceptive patch 7, 8, 9, 10. In 2002 Holt et al. (6) also demonstrated an association between higher body weight and increased risk of oral contraceptive (OC) failure in an analysis whose primary purpose was to examine the association between body weight and risk of OC failure. We used data from the 1995 National Survey of Family Growth (NSFG), a large survey of US women, to further investigate if increasing body weight is associated with OC failure in a retrospective cohort study.
Section snippets
Study Population and Design
The 1995 NSFG sample was drawn from respondents of the 1993 National Health Interview Survey (NHIS), a survey designed to provide information on the health of the civilian, noninstitutionalized, household population of the US. Through personal interviews with a national sample of women 15 to 44 years of age who responded to the 1993 NHIS, the NSFG aimed to collect more detailed data on factors affecting pregnancy and women's health. In 1995 trained personnel conducted interviews with 10,847
Results
The majority of study subjects were under 30 years of age, married, white, and well educated (Table 1). Hispanic and less educated women were at increased risk of OC failure (Table 2). Additionally, women with BMIs ≥ 30 had a statistically significant increased risk of having an OC failure as compared to women in the 20 to 24.9 BMI category (HR = 1.80, 95% CI, 1.01, 3.20). Results were similar when performed on the subpopulation of fecund and subfecund women (data not shown).
The Cox proportional
Discussion
In this study, we did not find a statistically significant association between increasing body weight or BMI and OC failure after adjustment for age, marital status, education, poverty level, race/ethnicity, parity, dual method use, and fecundity status.
The present study has several limitations. Nondifferential misclassification of the exposure is possible as weight was self-reported by the study participants. Though the validity of self-reported weight has been questioned, a number of studies
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No association between body size and frequency of sexual intercourse among oral contraceptive users
2014, Annals of EpidemiologyCitation Excerpt :In the context of contraceptive research interpretation, the risk of pregnancy is not influenced by method efficacy alone [2]. In particular, further examination of the possible association between body size and frequency of sexual intercourse may be important because studies of the obesity–oral contraceptive failure have been inconsistent [3–8], and many studies have been unable to adjust for this potentially important confounder [3,4,6–8]. Many women who use oral contraceptives are concerned that the use of this method will cause weight gain; however, a recent review found little evidence to support a strong association between oral contraceptive use and weight gain [9].
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