Abstract
OBJECTIVE: To evaluate from the literature whether combined hormonal contraception (CHC), including combined oral contraception pills (COCs), transdermal patch, vaginal ring or combined injectables, have different effectiveness or failure rates by body weight or body mass index (BMI). STUDY DESIGN: We searched PubMed and the Cochrane Library databases for all articles in all languages published between inception and February 2016, for evidence relevant to body weight or BMI, CHC use and contraceptive effectiveness. The quality of each individual study was assessed using the system for evaluating evidence developed by the United States Preventive Services Task Force. RESULTS: From 2874 articles, we identified 15 reports for inclusion, all of fair to poor quality. Fourteen studies measured the association of obesity status and contraceptive failure among COC users. Three fair quality and one poor quality study reported increased COC failure among a heterogeneous population of overweight and obese women compared with normal weight women, while eight fair quality and two poor quality studies did not find an association. Two fair quality studies reported on contraceptive transdermal patches. One pooled analysis described a higher proportion of pregnancies among women using the patch who weighed ≥90 kg; another secondary analysis suggested BMI>30 was associated with increased failure. No studies directly compared contraceptive effectiveness using the combined vaginal ring or combined injectable. CONCLUSION: Current available evidence addressing the risk of CHC failure in obese compared to normal weight women is limited to fair and poor quality studies. Studies of COCs show mixed results, though absolute differences in COC failure by body weight and BMI are small. Based on limited evidence, it appears that increasing body weight and BMI may contribute to decreasing contraceptive patch effectiveness.