Follicle monitoring is a continuous process, and a single examination cannot determine whether the follicles are developing and ovulating normally. The length of the menstrual cycle varies, so does the time to start follicle monitoring. If the time to start monitoring is not properly chosen, it is easy to miss the time of follicle development and fail to monitor follicle development, which may result in wrong judgment. Contents of ultrasound monitoring of follicular development It is required to measure the size of both ovaries, the number of follicles, their size, morphology, whether the borders are clear, and the internal echogenicity. Measurement of uterine size, morphology, echogenicity and intrauterine echogenicity are also required. The uterus should be measured for size, morphology and internal echogenicity. Measurement of follicle size requires measurement of 3 diameters in the largest section of the follicle, which must be monitored once a day for 2-3 days before ovulation. Monitoring time For 28-day menstrual cycles, monitoring usually starts on day 9-10 of the menstrual cycle; for 30-day cycles, monitoring can start on day 12-13; for menstrual cycles longer than 30 days, monitoring of follicular development starts from 16-18 days before the first day of the next menstrual period; drug-induced cycles require monitoring of follicular development 1-2 days in advance.