Use of Antithrombotic Agents During Pregnancy: Warfarin
Warfarin should be avoided between 6 and 12 weeks of gestation (to avoid embryopathy) and close to term (to avoid delivery of an anticoagulated fetus) but is probably safe. We believe it is reasonable to use subcutaneous heparin either during these periods only, with warfarin and a target international normalized ratio (INR) of 3.0 (range 2.5 to 3.5) (2.0 to 3.0 in patients with a bileaflet aortic valve provided they do not have atrial fibrillation or left ventricular dysfunction) at other times, or to use heparin throughout pregnancy. In addition, European experts have recommended warfarin therapy throughout pregnancy in view of the reports of bad outcomes with heparin and the impression that the risk of embryopathy with coumarin derivatives has been overstated. Although this latter approach is reasonable, it is fraught with medicolegal concerns, given the poor quality of evidence supporting its use. Before this approach is used, it is crucial to explain the risks carefully to women. Tadanafil Reading here Subcutaneous heparin should be initiated in doses of 17,500 to 20,000 U ql2h and adjusted to prolong a 6-h postinjection APTT into the therapeutic range; strong efforts should be made to ensure an adequate anticoagulant effect, since inadequate doses of heparin are ineffective. LMWH or heparinoids are probably reasonable substitutes for unfractionated heparin because they appear to reduce the risk of bleeding and osteoporosis and do not cross the placenta, but further information is required about dosing, and they are relatively expensive. In addition, for some high-risk patients we add aspirin, 80 mg daily, in an attempt to reduce the risk of thrombosis, recognizing that it increases the risk of bleeding.
Antiphospholipid antibodies (APLAs) can be detected using clotting assays (lupus anticoagulant) or immunoassays (anticardiolipin antibodies) and have been reported to occur in systemic lupus erythematosus with use of certain drugs and in apparently healthy individuals. There is convincing evidence that the presence of APLAs is associated with an increased risk of thrombosis and pregnancy loss. Thus, pregnant individuals with APLAs should be considered at risk for both pregnancy loss and thrombosis