Intended for healthcare professionals

Clinical Review ABC of antithrombotic therapy

Antithrombotic therapy in special circumstances. I—pregnancy and cancer

BMJ 2003; 326 doi: (Published 04 January 2003) Cite this as: BMJ 2003;326:37
  1. Bernd Jilma,
  2. Sridhar Kamath,
  3. Gregory Y H Lip

    Antithrombotic therapy during pregnancy

    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

    • Prophylaxis and treatment of venous thromboembolism

    • Prophylaxis in patients with valvar disease (for example, mitral stenosis)

    • Prophylaxis in patients with mechanical prosthetic valves

    • Antiphospholipid syndrome

    • Prophylaxis against pregnancy induced hypertension and intrauterine growth retardation

    Potential risks of antithrombotic therapy during pregnancy

    Maternal disadvantages and risks

    Unfractionated heparin

    • Haemorrhage (uteroplacental, especially during labour)

    • Heparin induced thrombocytopenia

    • Osteoporosis

    • Regular monitoring

    Low molecular weight heparin

    • Bleeding risk, especially during labour


    • Bleeding

    • Regular monitoring

    Risk to the fetus or child


    • Seems to be safe

    Low molecular weight heparin

    • Seems to be safe


    • Embryopathy, especially if mother is exposed between 6 and 12 weeks

    • Central nervous system malformations during any time of the gestation

    Low dose aspirin

    • Potential risk of birth defects and bleeding risk in the first trimester Embedded Image Safe in second and third trimester

    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 …

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