Although clinical trials report few...

Although clinical trials report fewer than 05 pregnancies by 100 women-years of use, pregnancy rates among patients who use oral contraceptives can be as high as seven by 100 women-years. An estimated 400000 pregnancies come about in the United States annually among oral contraceptive users. Preliminary studies prompt that body mass index (BMI) could contribute to oral contraceptive failure from one side an impact on steroid hormone metabolism. To clarify the character of body weight Holt and colleagues studied women who became pregnant while using oral contraceptives.

The authors used clinical data from enrollee of a large health maintenance organization to identify women who proofed positive for pregnancy within three month of filling an oral contraceptive prescription. The 546 women who agreed to participate in the close attention were interviewed. Those who had discontinued oral contraceptive use before becoming pregnant and those who reported missing five or more pills in the month of conception were exclud The 248 women who conceived while using oral contraceptives were matched by means of age with the control clump of 533 sexually active women who also filled prescriptions for oral contraceptives during the thought All participants were interviewed to obtain demographic, reproductive, medical, and lifestyle information. For the treatment arrange prepregnancy weight and a detailed pattern of oral contraceptive use during the month of conception were confirmed during the interview.

The pregnancy rate for oral contraceptive users was calculated as 28 by 1,000 women-years. Women who became pregnant were more likely to be black, married, smoker and to have had previous pregnancies. They were five times more likely to have previously conceived while using oral contraceptives. Women who became pregnant also had lower education on a levels and lower family income than women in the check group. The mean BMI for pregnant oral contraceptive users was 263 compared with 249 for women in the dominion government group. In logistic analysis controlling for other significant factors, the risk of oral contraceptive failure increased dramatically in same obese women. For women with BMI greater than 273 the pregnancy risk was 60 percent greater than in women with BMI of 213 or les The risk associated with BMI greater than 273 was flat stronger when the analysis was restricted to women who consistently used oral contraceptives correctly. The authors decide that the risk of oral contraceptive failure was significantly elevated in women with BMI of 273 or greater. In these obese women the risk of pregnancy, equal when using oral contraceptives consistently, was doubled. Biologic explanations for this observation include higher basal metabolic rate, induction of hepatic enzyme and increased sequestration of lipophilic hormones in adipose tissue. The authors calculate that obesity could add couple to four pregnancies per 100 woman-years of oral contraceptive use.

ANNE D WALLING, MD Holt VL et al. dead body mass index, weight, and oral contraceptive failure risk. Obstet Gynecol January 2005;105:46-52

COPYRIGHT 2005 American Academy of Family Physicians

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