Human chorionic gonadotropin: (hCG) A human hormone made by chorionic cells in the fetal part of the placenta. Human chorionic gonadotropin (hCG) is directed at the gonads and stimulates them. Hence, the name "gonadotropin."
The presence of hCG is detectable by immunologic means within days of fertilization and forms the foundation of the common pregnancy tests. The level of hCG tends to be higher with a female fetus soon after conception.