The timing of ovulation monitoring is related to the menstrual cycle and there are some individual differences, which need to be determined on a case-by-case basis. If you have regular menstrual periods, you can start follicle testing on day 9-10 of your menstrual cycle and monitor the dominant follicle once every other day. When the follicle diameter reaches 18-20mm, ovulation is imminent. If the follicle diameter exceeds 18mm and the endometrium exceeds 8mm, and the follicle still does not rupture, hCG can be injected as prescribed by the doctor, and ovulation usually occurs after 36 hours of medication.