The function of the corpus luteum of the ovary is to secrete a large amount of progesterone after fertilization, which in turn promotes the development of the embryo; the corpus luteum atrophies when fertilization does not occur, and menstruation occurs. The material that remains in the uterine cavity after ovulation in a normally functioning ovary is called the corpus luteum; if the egg cell is not fertilized after ovulation, the corpus luteum atrophies in about 10-12 days, and the secretion of estrogen and progesterone decreases, resulting in the shedding of the uterine lining, which leads to the onset of menstruation. If, after the formation of the corpus luteum, an egg cell meets a sperm and develops into a fertilized egg, the corpus luteum promotes the development of the fertilized egg and provides hormonal support for it. Abnormal function of the corpus luteum can cause irregular menstruation and, in early pregnancy, recurrent miscarriage or miscarriage with preeclampsia. The corpus luteum is a normal part of the ovary and should be treated if it becomes abnormally large.