Stasis, Hypercoagulability and vascular trauma( Virchow's triad) occurs in pregnancy and thus increases the risk of thrombsosis. Hypercoagulability is due to: Increase in Fibrinogen, prothrombin and factors VII,VIII,IX & X Decrease in levels of protein S. Resistance to activated protein C. Increase in levels of antifibrinolytic Types 1 & 2, plasminogen activator inhibitor PAI type 1 & 2. The net result is reduction in the risk of antepaum, intrapaum and postpaum hemorrhage but also a dramatic 10 fold increase in the pregnancy associated thromboembolism.