What is the role of progesterone in the menstrual cycle?

The primary role of progesterone is to thicken the lining of the uterus in order to prepare for pregnancy. It thickens the endometrium that allows for implantation of the embryo. The progesterone also inhibits secretion of FSH (Follicle stimulating hormone) that causes a new follicle to grow in the ovary in the case of pregnancy.Progesterone is secreted by the corpus luteum, however if pregnancy occurs it is secreted by the placenta throughout pregnancy.