Women with antithrombin (AT) III deficiency are prone to pregnancy-associated venous thromboembolism. We report 2 cases with genetically confirmed ATIII deficiency, one with a mutation in exon 3A and the other with an exon 4 deletion, in whom the pregnancies were successfully managed with prophylactic therapies for thrombosis. A 35-year-old pregnant woman was treated with intravenous infusions of ATIII concentrate alone, and the other 22-year-old pregnant woman was mainly treated with subcutaneous injections of heparin and oral low-dose aspirin therapy. Both pregnancies resulted in vaginal deliveries of healthy neonates. The literature concerning prophylactic therapies for thrombosis in ATIII deficiency-complicated pregnancy is reviewed, and the clinical problems, including the adverse effects of the therapies, are discussed.