It is necessary to monitor follicles during the preparatory stage of pregnancy, as a woman cannot conceive without healthy and mature follicles being released. Follicle monitoring is usually done on day 9-10 of the menstrual cycle, usually every other day, to understand the development of the follicles until the mature follicles are expelled. Follicle monitoring usually requires the use of vaginal ultrasound, which can show the development of the follicles more clearly and accurately. The normal diameter of a mature follicle is between 18 and 25 millimeters. When a follicle is mature enough to be discharged before intercourse, the chances of pregnancy are higher. Therefore, follicle monitoring is needed to check the development of the follicles to improve the chances of pregnancy. Those whose follicle monitoring results show abnormal development should be regulated under the guidance of a doctor.