Human chorionic gonadotropin

• Human chorionic gonadotropin (hCG) is a heterodimeric protein hormone that shares a common α-subunit with luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH), but has a unique β-subunit. It is most closely related to LH.
  
• Human CG is produced exclusively by the syncytiotrophoblast cells and can be detected in maternal serum 8–9 days after conception. It is the basis of all standard pregnancy tests.
  
• Human CG levels double every 48 hours in the first several weeks of pregnancy, reaching a peak of 80,000–100,000 mIU/mL at around 8–10 weeks’ gestation. Thereafter, hCG concentrations fall to 10,000–20,000 mIU/mL, and remain at that level for the remainder of pregnancy.
  
• The primary function of hCG appears to be maintenance of progesterone production from the corpus luteum of the ovary, until the placenta can take over progesterone production at around 6–8 weeks’ gestation. Progesterone is essential for early pregnancy success, eg, surgical removal of the corpus luteum or administration of a progesterone receptor antagonist (such as RU 486, mifepristone) before 7 weeks (49 days) of gestation will cause abortion.
  
• Human CG also has thyrotropic activity (0.025% of TSH), which only becomes clinically significant if hCG levels are markedly elevated such as in complete molar pregnancies.

Human chorionic somatolactotropin

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