Antithrombotic therapy in special circumstances. I—pregnancy and cancer
BMJ 2003; 326 doi: https://doi.org/10.1136/bmj.326.7379.37 (Published 04 January 2003) Cite this as: BMJ 2003;326:37- Bernd Jilma,
- Sridhar Kamath,
- 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
Warfarin
Bleeding
Regular monitoring
Risk to the fetus or child
Heparin
Seems to be safe
Low molecular weight heparin
Seems to be safe
Warfarin
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 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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