Abstract
Since their introduction, oral contraceptives have been linked to an increased incidence of thromboembolic events. Epidemiologic studies have shown that women who use third-generation oral contraceptives containing desogestrel, gestodene, or norgestimate have a higher risk of venous thrombosis than women who use second-generation oral contraceptives containing levonorgestrel. Women who use oral contraceptives are significantly less sensitive to activated protein C. From January 1996 to December 2001, 17,577 patients were hospitalized in our department, 177 of them (1%) had confirmed diagnosis of venous thromboembolism and 15 of those (177) were women on oral contraceptive therapy. Oral contraceptives were taken from 28 days to 18 months. No other potential congenital or acquired causes of thrombosis were present before thromboembolic events occurred in these women. The discontinuation of the pill combined with usual heparin (in one patient thrombolysis) and coumarin therapy was effective in all cases. After the discontinuation of coumarin (3-6 months), every patient was screened for hereditary thrombophilia. All women on oral contraceptive therapy had confirmed hereditary risk factors for venous thrombosis. Acquired resistance to activated protein C may explain the epidemiologic observation of increased risk of venous thrombosis in oral contraceptive users, especially in women using third-generation oral contraceptives who had other risk factors (hereditary or acquired) for venous thrombosis.