Infarction, and Stroke Among Transdermal Contraceptive System Users

OBJECTIVE: To estimate the incidence of venous throm-boembolism, acute myocardial infarction, and ischemic stroke among transdermal contraceptive system users compared with users of norgestimate-containing oral contraceptives with 35 mcg ethinyl estradiol. METHODS: We began with insurance claims data from UnitedHealthcare. We identified women exposed to the transdermal contraceptive system or norgestimate-con-taining oral contraceptives from April 2002 through De-cember 2004. Outcomes were confirmed from medical records. We calculated incidence rates and age-adjusted incidence rate ratios. In a nested case-control analysis, we investigated and controlled for confounding. RESULTS: There were 49,048 woman-years of transder-mal contraceptive system exposure and 202,344 woman-years of norgestimate-containing oral contraceptives ex-posure. There was a more than two-fold increase in the venous thromboembolism rate (incidence rate ratio 2.2, 95 % confidence interval [CI] 1.3–3.8) among transdermal contraceptive system users (20 cases, 40.8 per 100,000 woman-years) compared with norgestimate-containing oral contraceptives users (37 cases, 18.3 per 100,000 woman-years). Acute myocardial infarction occurred in three transdermal contraceptive system users compared with seven among norgestimate-containing oral contra-ceptives users (incidence rate ratio 1.8, 95 % CI 0.5–6.8). No strokes occurred among transdermal contraceptive sys-tem users, whereas 10 occurred among norgestimate-con-taining oral contraceptives users. In the nested case-control analysis, after exclusions for high-risk factors, the odds ratio for venous thromboembolism was 2.4 (95 % CI 1.1–5.5). CONCLUSION: There was a more than two-fold in-crease in the risk of venous thromboembolism associated with use of the transdermal contraceptive system. Acute myocardial infarction and stroke occurred too rarely to ascertain precise risk estimates