HCG (human chorionic gonadotropin) is a hormone produced by the placenta, and it is typically present only during pregnancy. It is commonly used to confirm pregnancy. Additionally, when combined with a progesterone test, hCG levels can help diagnose an ectopic pregnancy, assess the health of a pregnancy that may be at risk, and monitor a woman following a miscarriage. This test provides valuable information to help guide clinical decisions during early pregnancy or in cases of pregnancy complications.