Hereditary Antithrombin Deficiency Presenting with Deep Venous Thrombosis During the Second Pregnancy

A 37-year-old woman developed deep venous thrombosis (DVT) of the left lower extremity at 8 weeks of gestation during her second pregnancy. There was no personal or family history of thrombosis. She received intravenous heparin, but heparin resistance was noted. The plasma antithrombin activity decreased to 45% in the acute phase, and it remained low postpartum. Her mother also had low plasma antithrombin activity (46%), and genetic testing revealed a heterozygous SERPINC1 mutation. Even without a family history of thrombosis, we should suspect hereditary antithrombin deficiency in patients with initial DVT and perform thorough investigation.