WHAT: The luteal phase begins after ovulation and ends with the start of menstruation. During the luteal phase, the follicle becomes a corpus luteum. The corpus luteum produces estrogen and large amounts of progesterone which prepare the endometrium (the lining of the uterus) for implantation of a fertilized egg. If conception doesn’t occur, the corpus luteum disintegrates causing the endometrium to shed and a new menstrual cycle begins. The luteal phase lasts about 14 days and is remarkably consistent from woman to woman.