Pregnancy-specific beta-1-glycoprotein 3 is also known as Carcinoembryonic Antigen SG5,Pregnancy-Specific Glycoprotein 3 ,PS-Beta-G-3, PSBG-3.It belongs to the immunoglobulin superfamily. CEA family.It synthesized in large amounts by placental trophoblasts and released into the maternal circulation during pregnancy. Molecular cloning and analysis of several PSG genes has indicated that the PSGs form a subgroup of the carcinoembryonic antigen (CEA) gene family, Members of the CEA family consist of a single N domain, with structural similarity to the immunoglobulin variable domains, followed by a variable number of immunoglobulin constant-like A and/or B domains.