Hereditary antithrombin III deficiency and pregnancy: report of two cases and review of the literature.

The pregnancy and the serum antithrombin III levels during the antenatal and postpartum period of two patients with hereditary antithrombin III deficiency is described. Both antithrombin III antigen and activity levels dropped to their lowest levels immediately after delivery. A review of the literature emphasizes the high risk for thromboembolism in patients with hereditary antithrombin III deficiency. Important considerations for the obstetrician concerning hereditary antithrombin III deficiency are discussed, including: 1) the need to therapeutically anticoagulate these patients postpartum, 2) the need to consider prophylactic anticoagulation throughout pregnancy especially in patients with a history of thrombosis, 3) the practical aspects of assaying antithrombin III in plasma rather than serum, 4) the normally low antithrombin III levels in normal newborns, and 5) the need to provide prepregnancy counseling, including information about the autosomal dominant inheritance of hereditary antithrombin III deficiency.