Summary During pregnancy the concentrations of many coagulation factors are increased what leads to a „physiological” hypercoagulability status and constitutes a natural protection against delivery hemorrhage. These changes may be conducive to venous thrombembolism. Antithrombin is one of the endogenous clotting inhibitors. As a serine protease, it inactivates thrombin and the efficiency of this reaction is intensified by heparin. Acquired antithrombin deficiency is caused by disseminated intravascular coagulation syndrome, deep vein thrombosis, neoplasms, nephritic syndrome, renal failure, liver diseases, long-term estrogen treatment, dialysis or extracorporeal circulation. There are also cases of inherited antithrombin deficiency which leads to thrombophilia. The following study presents a course of pregnancy and postpartum of a woman with deep vein thrombosis and acquired antithrombin deficiency, as well as the applied treatment. The legitimacy of routine assay of antithrombin activity and antithrombin supplementation in pregnant women with thrombosis was considered. This procedure may be helpful when dealing with obese pregnant patients as it is difficulty to identify and establish a therapeutic dose of heparin in their cases. Therapy guidelines for pregnant patients with thrombosis and acquired antithrombin deficiency have not been established yet.