HCG is a hormone.  It stands for human chorionic gonadotropin.  It’s biological role is to promote the corpus luteum during early phases of pregnancy and to promote the production of progesterone to prepare the uterus for a fetus.

Pregnancy tests detect levels of this hormone.  The level of this hormone is lower at early stages of pregnancy, 5-50 mIU/mL.  These increase with each week of pregnancy, from levels of 1000 to up to 200000.

HCG is similar to LH, a hormone that affects ovulation.  HCG is often used to help women with infertility.  The injection of HCG is used to promote maturation of eggs and ovulation.  Ovulation normally occurs about 36-40 hours after injection.  During IVF procedures, egg retrieval is normally done about 36 hours after HCG, before natural ovulation.

HCG is sometimes used in men to stimulate testosterone production.  It has also been linked to performance enhancement scandals in professional sports.