FRAMINGHAM, Mass.--(BUSINESS WIRE)--GTC Biotherapeutics, Inc. (“GTC”, Nasdaq: GTCB) announced today that ATryn® has completed enrollment in the pivotal study for the treatment of patients with hereditary antithrombin deficiency, or HD, undergoing high-risk surgical or childbirth procedures. As previously announced, the pivotal study has met the primary endpoint of demonstration of non-inferiority to plasma-derived antithrombin in preventing clinically relevant deep vein thromboses, or DVTs, or other thromboembolisms.