When a woman has regular menstruation and ovulation is normal, 14 days before her menstruation is the day of ovulation, and 5 days before and 4 days after her menstruation is the day of ovulation, so 10-20 days before a woman’s menstruation is the day of ovulation. If a woman has an endocrine disorder, such as luteal insufficiency, her ovulation period will be disturbed and cannot be determined by normal estimation. Luteal insufficiency is a condition in which the luteal phase is significantly shortened and menstruation occurs within 12 days after ovulation. In addition when a woman has diseases such as adenomyosis and endometrial polyps, they also tend to cause irregular bleeding from the vagina and it is not possible to determine the time of the onset of menstruation in women normally, so it is also not possible to determine the patient’s ovulation period. When such abnormalities occur, patients can monitor the growth and development of follicles through ultrasound to project the ovulation period.