The human placenta is a multihormonal endocrine organ that produces hormones, enzymes, and other molecules that support fetal survival and development. Pregnancy-specific beta-1-glycoprotein (PSBG, PSG) is a major product of the syncytiotrophoblast, reaching concentrations of 100 to 290 mg/l at term in the serum of pregnant women (Horne et al., 1976 [PubMed 971765]). PSG is a member of the immunoglobulin (Ig) superfamily (Watanabe and Chou, 1988 [PubMed 3257488]\; Streydio et al., 1988 [PubMed 3260773]).[supplied by OMIM, Oct 2009].
Rausch, Sammel, Takacs, Chung, Shaunik, Barnhart: "Development of a multiple marker test for ectopic pregnancy." in: Obstetrics and gynecology, Vol. 117, Issue 3, pp. 573-82, (2011) (PubMed).