Oral contraception and factor V Leiden mutation in relation to localization of deep vein thrombosis

Both pregnancy and oral contraceptive (OC) use are associated with a predominance of thrombosis in the iliofemoral vein, with a left-sided dominance. It is unknown, however, if third-generation OCs and factor V Leiden mutation increase this left-sided dominance. This question was investigated by reference to data on all discharges of women 18-49 years of age with the diagnosis of deep venous thrombosis from the 10 hospitals in Denmark's North Jutland and Viborg counties in 1985-93. 54 of the 55 such cases identified included information on the location of the thrombus. 18 women had factor V Leiden mutation and 1 had an antithrombin deficiency; 2 women with factor V Leiden mutation also had a protein S deficiency. 39 women (71%) had deep vein thrombosis in the left lower limb; thrombosis was located in the left iliofemoral vein in 31 of these cases. Logistic regression analysis revealed an increased risk of deep vein thrombosis in the left femoral vein among third-generation OC users compared with nonusers and users of other types of OCs. Left-side dominance was not associated with Factor V Leiden mutation. Larger studies are required to confirm these results.