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Randomized Controlled Trial
. 2009 Jun;79(6):424-7.
doi: 10.1016/j.contraception.2008.12.013. Epub 2009 Mar 4.

Association between efficacy and body weight or body mass index for two low-dose oral contraceptives

Ronald T Burkman  1 , Alan C Fisher, George J Wan, Christopher E Barnowski, Katherine D LaGuardia
Affiliations
Randomized Controlled Trial

Association between efficacy and body weight or body mass index for two low-dose oral contraceptives

Ronald T Burkman et al. Contraception. 2009 Jun.

Abstract

Background: This analysis investigated the association of oral contraceptive efficacy with body weight and body mass index (BMI) for hypothesis-generating purposes.

Study design: Data were from a randomized, parallel-group trial of 180/215/250 mcg of norgestimate (NGM)/25 mcg of ethinyl estradiol (EE) (given to 1671 women) and 1 mg of norethindrone acetate (NETA)/20 mcg of EE (given to 1139 women). Pregnancies were evaluated across BMI deciles and by BMI and body weight dichotomies. A Pearl index was calculated for each treatment group. The relative risk (RR) of pregnancy was calculated with a Cox proportional hazards model.

Results: The Pearl index for women who received NGM/EE was 2.36 [95% confidence interval (CI)=1.33-3.40]; for those who received NETA/EE, the Pearl index was 3.29 (95% CI=1.81-4.77). Consistent, weak positive associations between weight and pregnancy risk were found. Overall, for women with a BMI >or=25 kg/m(2) (compared with women with a BMI <25 kg/m(2)), the RR of pregnancy was 1.84 (95% CI=0.98-3.45); that for women who received NGM/EE was 1.39 (95% CI=0.57-3.40), whereas that for women who received NETA/EE was 2.49 (95% CI=1.01-6.13). For women with a body weight >or=70 kg (compared with women with a body weight <70 kg), the RR was 1.25 (95% CI=0.63-2.46); that for women who received NGM/EE was 1.41 (95% CI=0.56-3.54), whereas that for women who received NETA/EE was 1.12 (95% CI=0.40-3.12).

Conclusion: Women in the higher body weight or BMI category showed a small increase in the risk of pregnancy with these oral contraceptives, but this increase was not statistically significant overall or for either formulation studied.

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Comment in

  • BMI and OCP failure.
    Richman S. Richman S. Contraception. 2010 Feb;81(2):175; author reply 175. doi: 10.1016/j.contraception.2009.09.003. Epub 2009 Oct 8. Contraception. 2010. PMID: 20103461 No abstract available.

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