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.