Use of Antithrombotic Agents During Pregnancy

Anticoagulant therapy is indicated during pregnancy for the prevention and treatment of VTE; for the prevention and treatment of systemic embolism in patients with mechanical heart valves; and, often in combination with aspirin, for the prevention of pregnancy loss in women with APLAs or thrombophilia and previous pregnancy losses. Several questions concerning anticoagulant therapy remain unanswered. It appears that LMWH will largely replace UFH. Oral anticoagulants are fetopathic, but the true risks of the warfarin embryopathy and CNS abnormalities remain unknown. There is considerable evidence that warfarin embryopathy occurs only when oral anticoagulants are administered between the sixth week and the 12th week of gestation and that oral anticoagulants may not be fetopathic when administered in the first 6 weeks of gestation. Oral anticoagulant therapy should be avoided in the weeks before delivery because of the risk of serious perinatal bleeding caused by the trauma of delivery to the anticoagulated fetus. The safety of aspirin during the first trimester of pregnancy is still a subject of debate. There is a concern about the efficacy of UFH in the prevention of arterial embolism in pregnant women with mechanical heart valves. Finally, the optimum management of pregnant women with thrombophilia (and prior pregnancy loss and/or prior VTE) is unknown, but trials of anticoagulant therapy are ongoing. Because it is safe for the fetus, LMWH (or UFH) is the anticoagulant of choice during pregnancy for situations in which its efficacy is established. There is some doubt that heparin is effective for the prevention of systemic embolism in patients with mechanical heart valves. Low doses of heparin or poorly controlled heparin therapy are not effective in preventing systemic embolism in patients with mechanical heart valves.