Hereditary thrombophilia and fetal loss: a prospective follow-up study.

BACKGROUND As the placental vessels are dependent on the normal balance of procoagulant and anticoagulant mechanisms, inherited thrombophilia may be associated with fetal loss. OBJECTIVES We performed a prospective study to investigate the relation between inherited thrombophilia and fetal loss, and the influence of thromboprophylaxis on pregnancy outcome. PATIENTS AND METHODS Women were enrolled in the European Prospective Cohort on Thrombophilia (EPCOT). These included women with factor (F)V Leiden or a deficiency of antithrombin, protein C or protein S. Controls were partners or acquaintances of thrombophilic individuals. A total of 191 women (131 with thrombophilia, 60 controls) had a pregnancy outcome during prospective follow-up. Risk of fetal loss and effect of thromboprophylaxis were estimated by frequency calculation and Cox regression modelling. RESULTS The risk of fetal loss appeared slightly increased in women with thrombophilia without a previous history of fetal loss who did not use any anticoagulants during pregnancy (7/39 vs. 7/51; relative risk 1.4; 95% confidence interval 0.4, 4.7). Per type of defect the relative risk varied only minimally from 1.4 for FV Leiden to 1.6 for antithrombin deficiency compared with control women. Prophylactic anticoagulant treatment during pregnancy in 83 women with thrombophilia differed greatly in type, dose and duration, precluding solid conclusions on the effect of thromboprophylaxis on fetal loss. No clear benefit of anticoagulant prophylaxis was apparent. CONCLUSIONS Women with thrombophilia appear to have an increased risk of fetal loss, although the likelihood of a positive outcome is high in both women with thrombophilia and in controls.