Inherited thrombophilia and gestational venous thromboembolism.

Thromboembolic disease is a leading cause of maternal morbidity and mortality during pregnancy and the puerperium. To reduce the incidence of venous thromboembolism in pregnancy and improve outcomes, an individual risk stratification based on probability of thrombosis as a rationale for an individual risk-adapted prophylaxis is required. Within the past 10 years, a significant improvement in risk estimation has been achieved due to the identification of new genetic risk factors of thrombosis. In women without prior thrombosis, the presence of a heterozygous factor V Leiden or heterozygous G20210A mutation in the prothrombin gene is associated with a pregnancy-associated thrombotic risk of approximately 1 in 400. Thus, in pregnant carriers of either one of these mutations the risk of venous thromboembolism is low--indicating that pregnancy-associated thrombosis is multicausal, resulting from the interaction of combined defects. A combination of the two genetic risk factors can increase the risk to a modest level (risk 1 in 25). In women with a single episode of prior thrombosis associated with a transient risk factor, for example, surgery or trauma, and no additional genetic risk factor, the probability of a pregnancy-associated thrombosis appears also to be low. In contrast, in women with a prior idiopathic venous thrombosis who carry an additional hereditary risk factor or who have a positive family history of thrombosis, a high risk (>10%) can be expected, supporting the indication for active antepartum and postpartum heparin prophylaxis. Despite the remarkable progress in risk stratification, the absolute magnitude of risk in many cases is unknown and current recommendations remain empirical.