Which hormone is secreted in a woman if pregnancy has occurred?

If fertilization occurs and the foetus is implanted in the endometrium, the trophoblast cells of the developing placenta secrete a hormone called Human Crionic Gonadtrophic hormone (HCG). This hormone like LH maintains the corpus luteum and secretion of progesterone and estradiol by it. These two hormone check the breakdown of the endometrium of the uterus. The absence of menstrual bleeding is the earliest sign of pregnancy.