An ovum matures in the follicle during the proliferative phase. FSH also stimulates the ovary to produce increasing amounts of estrogen. This process is known as ovulation. The ovum then travels from the ovary down the fallopian tube, and into the uterus. During the secretory phase, progesterone makes the endometrial lining stronger and spongy in texture.
Progesterone also stimulates glands in the endometrium.
These glands produce uterine fluid, and their purpose is to support embryonic development if fertilization has occurred at or around the time of ovulation. Generally symptoms are worse during the last seven to ten days of the cycle, ending at or soon after the start of the menstrual period. In a woman who hasn't become pregnant, the level of progesterone peaks about a week after ovulation and then begins to drop along with the estrogen level. The flow of blood to the endometrium decreases, and its upper portion is broken down and shed during menstruation. At the same time, the corpus luteum withers.