Clinical Significance

HCG (human chorionic gonadotropin) is a glycoprotein hormone secreted by the trophoblast cells of the placenta, which is composed of two subunits, α and β. The individual subunits are not biologically active and can only function after forming a dimer through non-covalent bonding. The main function of HCG is to stimulate the conversion of the corpus luteum into the corpus luteum of pregnancy, while promoting the continuous secretion of estrogen and progesterone, maintaining the morphology of the endometrium, promoting the formation of the uterine meconium, and allowing the placenta to grow and mature, which is essential for maintaining pregnancy.
      HCG secretion starts 6 days after fertilization, and increases rapidly in early pregnancy, doubling every 36-48 hours, reaching a peak at about 10 weeks of gestation, continuing to decline after 1-2 weeks, and disappearing about 2 weeks after delivery if no placenta remains.