The special case of venous thromboembolism in pregnancy

Pulmonary thromboembolism remains a major cause of maternal death in the Western world. The frequency of antepartum deaths, including deaths in the first and second trimester, which can be associated with early pregnancy problems such as hyperemesis, is similar in number to the deaths occurring following delivery. Risk factors for deep vein thrombosis have been identified and include age > 35 years, operative delivery (particularly emergency Caesarean section), obesity and a personal or family history of thrombosis or thrombophilia. These risk factors should be used to guide administration of thromboprophylaxis during both pregnancy and the post-partum period, particularly after Caesarean section. Specific consideration towards thromboprophylactic agents is required. Warfarin crosses the placenta, is a known teratogen when used in early pregnancy and can also be associated with bleeding problems in the foetus, particularly at the time of delivery. Thus, warfarin has a limited use in the antenatal period and is usually only employed in patients such as those with artificial heart valves who require long-term anticoagulation. However, as warfarin does not cross the breast in any significant amount, it is suitable during breast feeding. In contrast, heparin does not cross the placenta or the breast therefore foetal problems are not associated with this treatment. However, heparin can be associated with problems such as heparin-induced osteoporosis, allergy and heparin-induced thrombocytopenia. The risk of some of these complications can be reduced by the use of low-molecular-weight heparins. When venous thromboembolism is suspected in pregnancy, it is critically important to obtain an objective diagnosis. This will include real-time or duplex ultrasound scan of the legs to elaborate the venous system, ventilation perfusion lung scan and, occasionally, venography. Treatment of established venous thromboembolism is similar to that in the non-pregnant patient and it is likely that low-molecular-weight heparins will play a major role in thromboprophylaxis in the future.