Thromboembolism in Pregnancy: Recurrence and Its Prevention

Fifteen to 25% of thromboembolic events in pregnancy are recurrent events. Women with a history of thrombosis have a three- to fourfold increased risk of recurrence when they are pregnant compared with when they are not. The risks are even higher postpartum. The rate of recurrent venous thromboembolic events without anticoagulation is 2.4% to 12.2%, whereas the rate with anticoagulation is 0% to 2.4%. Because the rates of recurrent thromboembolism can be reduced with anticoagulation, women with a history of thrombosis who are not on lifelong anticoagulation will likely require anticoagulation during pregnancy, or at least during the postpartum period. Women who are already on lifelong warfarin for the prevention of recurrent venous thromboembolism should be counseled about the teratogenic effects of warfarin and offered the opportunity to be converted to heparin before conception. During pregnancy, low-molecular-weight heparin, with fewer side effects and a longer half-life, is generally preferred over unfractionated heparin. Unfractionated heparin with its shorter half-life is generally preferred around the time of delivery. Women on antiplatelet medication for prevention of arterial thromboembolism may be converted to low-dose aspirin after conception and supplemented with low-dose heparin or low-molecular-weight heparin during pregnancy. Because current recommendations rely on case series and expert opinion, additional studies including randomized trials might enhance our ability to prevent recurrent thromboembolism in pregnancy.