HCG is a hormone produced during pregnancy. One of its functions is to ensure the growing fetus receives enough nutrients to grow and develop normally. It does this by making the excess fat stored in the mother's body available for use. The mother's body is then able to use this fat for nutrients and energy even with limited caloric consumption. This is why a women can suffer from "morning sickness" with symptoms such as daily vomitting for months at a time and the baby does not suffer. Pregnancy is the only time HCG is found in the body.