Thromboembolism remains a major cause of maternal morbidity and mortality. The incidence of thrombosis associated with pregnancy is stated to be around 0.09%1 but is greater in women with familial or acquired thrombophilia. Around 50% of pregnancies in women with antithrombin III deficiency are complicated by thrombosis. Anticoagulation throughout pregnancy and the puerperium is recommended in women with antithrombin III deficiency. Because thrombosis is less common in women with protein C or protein S deficiency less aggressive management may be appropriate during pregnancy but anticoagulation post partum is generally recommended. The most important acquired thrombophilic abnormality is the development of antiphospholipid antibodies ('lupus anticoagulants'). Women with these antibodies may present major problems but no clear guidelines for their management currently exist. The majority of women with a history of thrombosis have no identifiable haemostatic abnormality. Management of pregnancy in these patients depends on individual circumstances.