Venous thromboembolism, myocardial infarction, and stroke among transdermal contraceptive system users.Obstet Gynecol. 2007 Feb; 109(2 Pt 1):339-46.OG
To estimate the incidence of venous thromboembolism, acute myocardial infarction, and ischemic stroke among transdermal contraceptive system users compared with users of norgestimate-containing oral contraceptives with 35 mcg ethinyl estradiol.
We began with insurance claims data from UnitedHealthcare. We identified women exposed to the transdermal contraceptive system or norgestimate-containing oral contraceptives from April 2002 through December 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.
There were 49,048 woman-years of transdermal contraceptive system exposure and 202,344 woman-years of norgestimate-containing oral contraceptives exposure. 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 contraceptives users (incidence rate ratio 1.8, 95% CI 0.5-6.8). No strokes occurred among transdermal contraceptive system users, whereas 10 occurred among norgestimate-containing 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).
There was a more than two-fold increase 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.
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