Combined hormonal contraceptive use among obese women and risk for cardiovascular events: A systematic review

Context: Combined hormonal contraceptive (CHC) use may modify the risk of cardiovascular events in obese [body mass index (BMI) ≥30kg/m²] women.

Objective: The objective was to evaluate from the literature whether CHC use modifies the risk of acute myocardial infarction (AMI), stroke, cerebral venous thrombosis (CVT) and venous thromboembolism (VTE) in obese women and to evaluate evidence for a dose-response relationship between BMI and VTE.

Methods: We searched PubMed for all articles published between database inception and February 2016 providing direct evidence on BMI, CHCs, and cardiovascular outcomes. We also searched for indirect evidence related to a dose-response relationship between BMI and risk of VTE in the general population, as these data were lacking for CHC users. The quality of each individual study was assessed using the system for grading evidence developed by the United States Preventive Services Task Force.

Results: The direct evidence search yielded 3 pooled analyses, 11 case-control studies and 1 cohort study. There was conflicting evidence about the risk of AMI or stroke among obese combined oral contraceptive (COC) users compared to obese nonusers, with one study finding no increased risk for AMI or stroke for COC users overall or stratified by BMI. A second study found significantly increased risk of AMI and stroke for COC users, with the highest risk estimates for high-BMI COC users. A single study suggested that obese COC users may be at higher risk for CVT compared with normal-weight nonusers. For VTE, obese COC users consistently had a risk that was 5 to 8 times that of obese nonusers and approximately 10 times that of nonobese nonusers. Five prospective cohort studies were identified as indirect evidence, and all found increased risk for VTE as BMI increased, suggesting a dose-response relationship between BMI and risk for VTE. No studies on the contraceptive patch or vaginal ring were identified that met the inclusion criteria.

Conclusion: Limited evidence of Level II-2, fair quality, concerning whether CHC use modifies the risk of AMI and stroke in obese women is inconclusive, while a single study of Level II-2, poor quality, found that obese COC users may be at higher risk for CVT compared with normal-weight nonusers. Both COC use and higher BMI increase risk for VTE, and the greatest relative risks are for those with both risk factors based on a body of evidence graded as Level II-2, fair to poor quality. It is not possible to estimate absolute risk of VTE among women with both of these risk factors; however, the absolute risk of VTE in healthy women of reproductive age is small.