The dominant follicle is the one that can develop into a mature follicle and needs to be large enough, usually 15-20mm, with more follicular fluid and a larger follicular cavity, with the follicle protruding toward the ovarian surface. The rest of the follicles degenerate on their own through apoptosis at different stages of development, so the normal human pregnancy is singleton. Ovulation mostly occurs about 14 days before the next menstrual period, and after ovulation, she enters the luteal phase. Women in the luteal phase need to be careful to avoid strenuous exercise. Some women may experience acute abdominal pain and intra-abdominal hemorrhage due to the rupture of the corpus luteum after strenuous exercise.