Precautions for follicle monitoring include clarifying the timing of the test, ultrasound method, monitoring the largest follicle, projecting the ovulation period, and fixing the monitoring place and doctor. 1. Define the timing of the test: For women with regular menstrual cycles, it is recommended to start monitoring the follicle size on the 10th day of the menstrual cycle, but for those with long or disrupted menstrual cycles, it is recommended to start monitoring from the day after the menstrual cycle is cleared. 2. Ultrasound: For those who choose abdominal ultrasound, it is necessary to perform the examination after the bladder is full in order to be able to clearly show both ovaries and the number of follicles. Transvaginal ultrasound can also be chosen. 3. Monitoring the largest follicle: to clarify the number and size of follicles in both ovaries, to monitor the largest follicle and to determine whether it is in the left or the right ovary, in order to facilitate subsequent monitoring. 4. Estimation of ovulation period: Define the dominant follicle and start to monitor the follicle at intervals of 1~2 days from the time it reaches 12mm, the normal follicle grows by 1.6mm per day, and it can be up to 18~23mm before ovulation, and it can be discharged within 24~48 hours, then it can be monitored every day in order to define the time of ovulation, and it can be guided to have coitus. 5. Fixed monitoring place and doctor: It is recommended to monitor the process in the same hospital and try to be examined by the same doctor and the same instrument, which can reduce the monitoring error.