hCG, or human chorionic gonadotropin, is a hormone produced during pregnancy. It is secreted by the placenta shortly after a fertilized egg attaches to the uterine lining. hCG helps maintain the production of progesterone, which is essential for a healthy pregnancy. In addition to its role in pregnancy, hCG is also used in medical treatments. It can be prescribed to stimulate ovulation in women and to treat certain conditions in men, such as low testosterone levels. hCG is commonly detected in pregnancy tests, as its presence indicates that a woman is pregnant.