A glycoprotein hormone secreted by the PLACENTA in early pregnancy, and stimulating the CORPUS LUTEUM within the ovary (see OVARIES) to secrete OESTROGENS, PROGESTERONE, and relaxin. The hormone is essential for the maintenance of pregnancy up to about 6–8 weeks of gestation. A RADIOIMMUNOASSAY can be used to detect its presence, and pregnancy can be diagnosed as early as six days after conception by testing for it in the urine. Some tumours also secrete human chorionic gonadotrophin, particularly HYDATIDIFORM MOLE, which produces large amounts.