Ultrasound is very accurate in detecting follicles. Because the follicle growth has a certain pattern, at the beginning of the growth of 1-2 mm per day, to the time of ovulation growth of 2-5 mm per day, close to the time of ovulation, ultrasound can be dynamic observation of its size every day, through the presumption of judgment for normal growth of the follicle, and the accuracy of the measurement is very high. When monitoring ovulation, you can also monitor the basal body temperature, as well as monitoring hormone levels, etc., to determine the normal time of ovulation. Assuming that a woman’s cycle is 30 days long, it is generally recommended to start monitoring on day 12-14, when the follicles begin to grow faster, and to monitor every 1-2 days from this point on.