Ultrasound monitoring of follicles is clinically indicated by the following. Firstly, if the menstrual cycle is 30 days, it is recommended to start ultrasound monitoring of follicles from the 12th day of menstruation, mainly to find out if there are follicles growing in the ovaries. Secondly, on the 14th day of menstruation, an ultrasound will be done to find out if the original follicle has grown, which normally grows at a rate of 1.5-2mm per day. Then on the 16th day of menstruation, an ultrasound will be done to see if the original follicle has ruptured and expelled the egg. Thirdly, it is important to monitor the follicles, preferably by vaginal ultrasound, so that they can be seen more clearly. Fourthly, if the follicle has reached a clinical diameter of 25mm and still has not ruptured and expelled the egg. It is recommended to take another ultrasound every other day. If the follicle still does not rupture, it can be diagnosed as follicular flavinization. A detailed clinical examination is recommended and then, depending on the results, the appropriate treatment will be given.