Human chorionic gonadotropin (hCG) is a hormone produced by the placenta after implantation. It nourishes the egg when it fertilised and attaches the uterine wall.Due to its highly negative charge, hCG may repel the immune cells of the mother, protecting the fetus during the first trimester. It has also been hypothesized that hCG may be a placental link for the development of local maternal immunotolerance.