Serum and Chorionic Tissue Concentrations of Human Chorionic Gonadotropin and Its Subunits During Pregnancy

hCG, hCG-α and hCG-β in sera of pregnant women and in chorionic tissue weie radioimmunoassayed in respective homologous radioimmunoassay systems. hCG in sera showed a peak in the first trimester. Serum level of hCG-α increased gradually along the pregnancy, reaching maximum in the 36th week of gestation, and decreased toward parturition. hCG-β in sera, however, remained in a lower level throughout the pregnancy. All chorionic tissues contained high amounts of hCG and hCG-α, and a small of hCG-β, although the concentrations of those varied quantitatively with progress of the pregnancy. In chorionic tissue hCG-α and hCG-β might be respectively synthesized, and hCG might be produced by a combination of these subunits.