Human chorionic gonadotropin hormone HCG

• Facts:
  Secreted by the syncytiotrophoblast
  
  Preserves the corpus luteum during early pregnancy until the placenta is able to produce progesterone on its own
  
  Production begins about eight days after fertilization, levels double every 48hrs, peaking at six to eight weeks gestation
• Notes:
  Composed of two subunits (α and β)
  Alpha (α) subunit is common to hCG, TSH, LH, and FSH
  Beta (β) subunit is specific to hCG (pregnancy tests)