Case-control study of risk of cerebral sinus thrombosis in oral contraceptive users who are carriers of hereditary prothrombotic conditions

Objective: To investigate whether users of oral contraceptives who are carriers of a hereditary prothrombotic condition (factor V Leiden mutation, protein C, S, or antithrombin deficiency) have an increased risk of cerebral sinus thrombosis. Design: Comparison of a prospective series of cases of cerebral sinus thrombosis with population data. Setting: Neurological teaching hospitals from different regions in the Netherlands (cases) and a representative sample of the non-institutionalised Dutch population (controls). Subjects: 40 women aged 18-54 years with cerebral sinus thrombosis (cases) and 2248 women aged 18-49 years (controls). Main outcome measure: Current use of oral contraceptives at the time of the thrombosis (cases) or at the time of the questionnaire (controls). Prevalences of a hereditary prothrombotic condition in patients and in the population with odds ratios. Results: 34 of 40 (85%) women with cerebral sinus thrombosis used oral contraceptives, versus 1007 of 2248 (45%) of the control women; the age adjusted odds ratio was 13 (95% confidence interval 5 to 37). Seven of 36 patients (19%) had a prothrombotic deficiency, versus 7% expected in the population; this corresponds to a threefold to fourfold increase in risk. In women who used oral contraceptives and also carried a prothrombotic defect, the odds ratio for cerebral sinus thrombosis was about 30 relative to women who had neither risk factor. Conclusion: The use of oral contraceptives and being a carrier of a hereditary prothrombotic condition increase the risk of and interact in a multiplicative way in the development of cerebral sinus thrombosis.