Factor V Leiden: association with venous thromboembolism in pregnancy and screening issues.

Disturbances of the natural balance between procoagulant and anticoagulant mechanisms can result in bleeding or thrombotic tendencies. Factor V, on activation by thrombin to factor Va, forms an essential component of the prothrombinase complex, in which it demonstrates its cofactor activity for factor Xa. Down-regulation of factor Va by activated protein C (APC) occurs through cleavage of specific peptide bonds in the heavy chain of the molecule. Factor V Leiden (FV Leiden) is a mutation of factor V that renders factor Va resistant to APC, due to loss of one of these cleavage sites. This mutation predisposes the patient to thrombosis. Prevalence of FV Leiden varies; however, heterozygosity for the FV Leiden mutation is recognised as the most common heritable thrombophilic defect in Caucasian populations. The association this inherited thrombophilia has with venous thromboembolism (VTE) is well established. Pregnancy is notably an acquired hypercoagulable state, due in part to physiological changes that occur in the coagulation system. This seems to have potential for interaction with FV Leiden to cause adverse experiences. A role has been suggested for FV Leiden in VTE events during pregnancy. At present only selected women are screened for FV Leiden. Pregnant women with a history of VTE or with a family history of the mutation are investigated. Whether or not the introduction of a routine screening plan for this mutation is justified remains a matter for debate.