The best time to monitor follicles with ultrasound is usually from day 9 of the menstrual cycle until the eggs are expelled. The best time to monitor follicles with ultrasound is usually from day 9 of the menstrual cycle until the eggs are expelled. Follicle monitoring under ultrasound is the best way to monitor follicles at this stage because it is possible to clearly observe the growth and development of the follicles and whether they are expelled normally. There are two types of follicle monitoring under ultrasound, one for women with regular menstruation and the other for women with irregular menstruation, and the time frame for the test is different. For women with regular periods, the ovulation time will be more regular, so you can start monitoring from the 9th day of the menstrual cycle and keep monitoring until the follicles are successfully expelled. Women with irregular periods can monitor the development of follicles or the number of sinus follicles on day 3 of their menstrual cycle. Each subsequent test needs to be determined by the size of the follicles, and if no mature follicles have been monitored, this indicates abnormal ovulation. Testing follicles with ovulation test strips is subject to error, usually on the day when hormone levels are at their peak, and the test is done around day 14 to day 17 of the menstrual cycle. Alternatively, the size of the follicle can be detected by ultrasound, and the peak can be monitored by monitoring the test paper above 1.6 cm. Follicles are generally developed to between 20 by 22 mm as mature follicles, which also have the ability to conceive, so follicle monitoring has some clinical significance in improving a woman’s pregnancy rate.