A review published in the Cochrane Database of Systematic Reviews generally found no association between higher body mass index (BMI) or weight and hormonal contraceptive efficacy.

Study authors examined the efficacy of hormonal contraceptives in preventing pregnancy among women who are overweight or obese vs. women with a lower BMI or weight. They searched databases until August 4, 2016, as well as reference lists of relevant articles for studies that examined any type of hormonal contraceptive. Eligible studies included data on the specific contraceptive method used with a primary outcome of pregnancy. 

The main comparison was between overweight or obese women and women of lower weight or BMI. In addition, researchers used unadjusted pregnancy rates, relative risk (RR), or rate ratio where applicable. A total of 17 studies met the inclusion criteria, which included 63,813 women; 12 studies with high, moderate, or low quality evidence were included in the review. 

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The data showed most studies did not demonstrate a higher pregnancy risk among overweight or obese women. Among the five studies on combination oral contraceptives, two associated BMI with pregnancy but in opposite directions. Oral contraceptives containing norethindrone acetate and ethinyl estradiol were associated with a higher risk of pregnancy for women with BMI ≥25 (overweight) vs. those with BMI <25 (RR 2.49, 95% CI: 1.01-6.13). On the other hand, using an oral contraceptive containing levonorgestrel and ethinyl estradiol showed a Pearl Index of 0 for women with BMI ≥30 (obese) vs. 5.59 for women with BMI <30 (non-obese). 

The same study evaluated a transdermal patch containing levonorgestrel and ethinyl estradiol and found that obese women in the “treatment-compliant” subgroup had a higher reported Pearl Index vs. non-obese women (4.63 vs. 2.15). Among the five studies that evaluated implants, two studied the 6-capsule levonorgestrel implant and demonstrated differences in pregnancy based on weight. One study indicated that higher weight was associated with higher pregnancy rate in Years 6 and 7 combined (P<0.05). The other study found pregnancy rates varied in Year 5 among the lower weight groups only (P<0.01) and did not enroll women weighing ≥70kg. 

Moreover, there was no association seen between pregnancy and overweight or obesity for other contraceptive methods (eg, depot medroxyprogesterone acetate [subcutaneous], levonorgestrel intrauterine contraceptive, the 2-rod levonorgestrel implant, the etonogestrel implant).

Studies using BMI vs. weight alone offer information about whether body composition is associated with contraceptive efficacy. In general, the overall quality of evidence was low for the objectives of the review. Future studies should include more overweight or obese women in order to examine the effects of these drugs in these patient populations.

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