Thromboembolism

The overall incidence of venous thromboembolism is about 0.7 per thousand maternities, but pulmonary embolus is currently the single most common cause of maternal mortality. Major risk factors are operative delivery, age, multiparity and previous thromboembolism. Because of the risks in anticoagulant therapy and the difficulties of clinical diagnosis, it is essential to use objective tests, usually venography for deep-vein thrombosis and lung scan for pulmonary embolus. The acute phase will normally be treated with a continuous infusion of heparin, followed by subcutaneous heparin, given until at least six weeks post-delivery. Warfarin may be substituted after the first week post-delivery. In contrast to the treatment of other forms of thromboembolism, patients with artificial heart valves should be managed with warfarin until 36 weeks of pregnancy. Although the fetal risks in warfarin therapy are greater than those of subcutaneous heparin, the obvious alternative, subcutaneous heparin, does not provide adequate prophylaxis against thromboembolism.

In patients who have had venous thromboembolism in the past, the maternal risks do not justify prolonged prophylaxis with subcutaneous heparin as usually given (20000 units per day) throughout pregnancy. Further clinical trials are necessary to select the best alternatives.

Antithrombin III deficiency should be managed with subcutaneous heparin taken from before conception until at least one week post-delivery, when warfarin therapy can be recommended. In addition, the labour should be covered with antithrombin III concentrate.