Human chorionic gonadotropin (HCG) is a glycoprotein hormone consisting of two noncovalently bonded subunits, alpha and beta [PMID: 68892], and is normally synthesized by placental trophoblasts during pregnancy. The alpha subunit of hCG is identical to the alpha subunit of 3 hormones synthesized by the anterior pituitary gland but the beta subunit of each of these hormones is unique and confers biological specificity. CGA is mainly used for the diagnosis and adjuvant diagnosis of placental trophoblast and germ cell tumors such as hyperemesis gravidarum and choriocarcinoma.