The human pregnancy-specific glycoproteins (PSGs) are a family of proteins that are 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, which belongs to the immunoglobulin superfamily of genes. 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. Most PSGs have an arg-gly-asp (RGD) motif, which has been shown to function as an adhesion recognition signal for several integrins, in the N-terminal domain (summary by Teglund et al., 1994 [PubMed 7851896]). For additional general information about the PSG gene family, see PSG1 (MIM 176390).