Pregnancy, the postpartum period and prothrombotic defects: risk of venous thrombosis in the MEGA study.

BACKGROUND Venous thrombosis is one of the leading causes of maternal morbidity and mortality. OBJECTIVE In the MEGA study, we evaluated pregnancy and the postpartum period as risk factors for venous thrombosis in 285 patients and 857 control subjects. PATIENTS/METHODS Between March 1999 and September 2004, consecutive patients with a first episode of venous thrombosis were included from six anticoagulation clinics. Partners of patients and a random digit dialing group were included as control subjects. Participants completed a questionnaire and DNA was collected. RESULTS The risk of venous thrombosis was 5-fold (OR, 4.6; 95% CI, 2.7-7.8) increased during pregnancy and 60-fold (OR, 60.1; 95% CI, 26.5-135.9) increased during the first 3 months after delivery compared with non-pregnant women. A 14-fold increased risk of deep venous thrombosis of the leg was found compared with a 6-fold increased risk of pulmonary embolism. The risk was highest in the third trimester of pregnancy (OR, 8.8; 95% CI, 4.5-17.3) and during the first 6 weeks after delivery (OR, 84.0; 95% CI, 31.7-222.6). The risk of pregnancy-associated venous thrombosis was 52-fold increased in factor V Leiden carriers (OR, 52.2; 95% CI, 12.4-219.5) and 31-fold increased in carriers of the prothrombin 20210A mutation (OR, 30.7; 95% CI, 4.6-203.6) compared with non-pregnant women without the mutation. CONCLUSION We found an increased risk of venous thrombosis during pregnancy and the postpartum period, with an especially high risk during the first 6 weeks postpartum. The risk of pregnancy-associated venous thrombosis was highly increased in carriers of factor V Leiden or the prothrombin 20210A mutation.