Third generation oral contraceptives and risk of venous thromboembolic disorders: an international case-control study

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Abstract
Objective: To test whether use of combined oral contraceptives containing third generation progestogens is associated with altered risk of venous thromboembolism. Design: Matched case-control study. Setting: 10 centres in Germany and United Kingdom. Subjects: Cases were 471 women aged 16-44 who had a venous thromboembolism. Controls were 1772 women (at least 3 controls per case) unaffected by venous thromboembolism who were matched with corresponding case for age and for hospital or community setting. Main outcome measures: Odds ratios derived with stratified analyses and unconditional logistic regression to adjust for potential confounding variables. Results: Odds ratios (95% confidence intervals) for venous thromboembolism were: for any oral contraceptives versus no use, 4.0 (3.1 to 5.3); for second generation products (low dose ethinyloestradiol, no gestodene or desogestrel) versus no use, 3.2 (2.3 to 4.3); for third generation products (low dose ethinyloestradiol, gestodene or desogestrel) versus no use, 4.8 (3.4 to 6.7); for third generation products versus second generation products, 1.5 (1.1 to 2.1); for products containing gestodene versus second generation products, 1.5 (1.0 to 2.2); and for products containing desogestrel versus second generation products, 1.5 (1.1 to 2.2). Probability of death due to venous thromboembolism for women using third generation products is about 20 per million users per year, for women using second generation products it is about 14 per million users per year, and for non-users it is five per million per year. Conclusions: Risk of venous thromboembolism was slightly increased in users of third generation oral contraceptives compared with users of second generation products. Key messages This case-control study examined risk of venous thromboembolism associated with different types of oral contraceptive Overall, there was a fourfold higher relative risk of thromboembolism associated with current use of any oral contraceptive versus no current use The risk of thromboembolism was 1.5 times higher for third generation contraceptives compared with second generation products Our data indicate the need for clinical prudence but allow doctors and women seeking contraception to exercise informed choice