Clotting defects raise risk of venous thrombosis from the Pill
CMAJ 2000;162:1197
Venous thrombosis develops more often and sooner in women taking oral contraceptives who have inherited clotting defects than in women without these defects, according to a study that identifies a major risk factor for women taking the Pill (Arch Intern Med 2000;160:49-52). The study confirms findings from previous studies showing that deep venous thrombosis occurs more often during the first year — and especially the first 6 months — of oral contraceptive use. It also shows that women with inherited clotting defects — protein C deficiency, protein S deficiency, antithrombin deficiency, factor V Leiden mutation or prothrombin 20210 A mutation — have a risk of deep venous thrombosis 11 times higher than other women in their first year on the Pill, and 19 times higher in the first 6 months. While the authors say it is "uncertain" whether women should be screened for genetic clotting disorders before starting oral contraceptives, they recommend taking a careful family history and providing patients with information about the signs and symptoms of venous thrombosis. An occurrence of venous thrombosis in a woman taking oral contraceptives may mean that she has a clotting disorder.
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