Antithrombotic therapy in special circumstances. I—pregnancy and cancer

Pregnancy predisposes to venous thromboembolism for several reasons. These include a change in the balance between procoagulant and anticoagulant factors in the blood. Any conditions that predispose a woman to thromboembolism when she is not pregnant will also predispose her to thromboembolism when she is pregnant. #### Disorders during pregnancy for which antithrombotic therapy is commonly considered #### Potential risks of antithrombotic therapy during pregnancy ##### Maternal disadvantages and risks Unfractionated heparin Low molecular weight heparin Warfarin ##### Risk to the fetus or child Heparin Low molecular weight heparin Warfarin Low dose aspirin Generally, antithrombotic therapy started in a non-pregnant patient for a particular disorder needs to be continued during the pregnancy and in the puerperium. The use and type of antithrombotic therapy depends on the risk:benefit ratio, taking into consideration the potential harm to the mother and the fetus. The potential risks of antithrombotic therapy during pregnancy can be divided into maternal and fetal risks, and include teratogenicity and bleeding. Unfractionated heparin and low molecular weight heparins do not cross the placenta and are probably safe for the fetus, although bleeding at the uteroplacental junction is possible. Nevertheless, data are sparse for low molecular weight heparin, with no reliable comparative trials or convincing dose assessment. In contrast to heparin, coumarin derivatives cross the placenta and can cause both bleeding in the fetus and teratogenicity. Coumarin derivatives can cause an embryopathy …