Coagulation changes occur during pregnancy, and result in increased risk of VTE. Pharmacologic interventions, such as heparin, help prevent VTE through effects on the clotting cascade. Both low-molecular-weight heparin and unfractionated heparin bind to antithrombin, catalyzing its binding to and inactivation of procoagulant molecules. Candidates for prophylactic anticoagulation during pregnancy include women with a history of thrombosis or a high-risk thrombophilia, but routine anticoagulation is not recommended for all pregnant women due to the risk of bleeding complications.
Stasis is reduced blood flow through the veins. In the case of pregnancy-related VTE, it is primarily in the veins of the legs. Several factors increase venous stasis in the pregnant woman. Venous stasis increases during pregnancy due to hormonally induced decrease in venous dilation, reduced venous outflow due to compression caused by veins being obstructed by the enlarged uterus, and increased intravascular volume that distends veins. Stasis may also be related to prolonged periods of immobility such as bed rest which may be indicated during pregnancy due to high-risk conditions.
Intermittent pneumatic compression devices are designed to reduce venous stasis through regular compression of the leg and promote clearance of the deep veins without the risk of distal blood trapping. Intermittent pneumatic compression devices are clinically proven to reduce the risk of VTE in non-OB surgical patient populations. The American College of Obstetricians and Gynecologists recommends placement of pneumatic compression devices before Cesarean delivery for all women not already receiving thromboprophylaxis.
Vessel wall damage also increases the risk of VTE. Graduated compression stockings help prevent pooling of blood in the legs. Correct fit is essential because improperly fitted stockings may increase venous stasis. Graduated compression stockings have been found to be more effective when combined with a second form of prophylaxis.