Anticoagulant Therapy of Pregnant Patients with Prosthetic Heart Valves : Rationale for a Clinical Trial of Low Molecular Weight Heparin

The management of anticoagulant therapy for the prevention of thromboembolism from prosthetic heart valves in the pregnant patient is far from ideal and deserves more clinical research. Warfarin therapy given alone throughout pregnancy poses high risks to the fetus because it crosses the placental barrier. Heparin alone throughout pregnancy poses high risks to the mother, which might be lessened somewhat by more intensive therapeutic regimens and careful monitoring of the heparin level or anticoagulated state of the blood. Because of the major risk of embryopathy in the fetus during the first trimester and latter half of the third trimester, heparin therapy during those times has been recommended. In the opinion of some experts, high-risk cases may benefit from low-dose aspirin in addition to anticoagulant therapy. The fact that warfarin is contraindicated during pregnancy (according to the pharmaceutical company that markets it) poses some problems for the physician who prescribes it. For the above reason, alternative drugs are worthy of consideration and should be given clinical trials. Low molecular weight heparin has the potential for greatly reducing drug-related risk for the fetus while providing greater safety for the mother.