It is more appropriate to monitor the follicles on the 9th to 10th day of menstruation. Usually, based on a 28-day menstrual cycle, a woman’s day of ovulation is in the middle of two menstrual periods, i.e., about 14 days before the next period, and there are still 4 to 5 days to go before the day of ovulation on the 9th to 10th day of menstruation, when follicles can be seen to be growing, and it is easy to judge whether the follicles are developing normally or not and whether they are dominant or not, therefore, it is more suitable for follicle monitoring on the 9th to 10th day of menstruation. Follicle monitoring is mainly done through ultrasound to observe whether the follicles are developing well and whether there is ovulation. Women who have been preparing for pregnancy for more than a year but have not yet gotten pregnant, especially those with irregular periods, can undergo a one-month ultrasound to monitor and observe the follicle growth process, so as to increase the possibility of pregnancy. Women with fertility needs who need to monitor their follicles should be evaluated by a doctor on an individual basis to determine the appropriate time for follicle monitoring. If you have any other questions, please consult your doctor.