Progesterone is a steroid hormone secreted by a yellow endocrine gland, corpus luteum, formed from empty Graafian follicle during the pregnancy. A small amount of progesterone is also secreted by adrenal cortex and placenta. It stimulates the proliferation of endometrium of the uterus and prepares it for implantation. It also helps in implantation, placenta formation and normal development of the foetus in the uterus.