Ultrasound examination is possible to monitor ovulation. Currently, the common clinical methods used to detect follicular ovulation are, firstly, ultrasonography and secondly, basal body temperature measurement, among which ultrasound has certain advantages in monitoring ovulation. Ultrasound examination allows real-time observation of all changes in follicle size and morphology, including dominant follicles, mature follicles, post-ovulatory follicles, and retained follicles. Ultrasound monitoring of ovulation can be done every 1-2 days starting from the 10th day of menstruation if the menstruation is usually regular, to monitor the follicle development until ovulation. The signs of ovulation are the dominant follicle and mature follicle visible on continuous observation, and the diagnosis can be made when the follicle shrinks or the follicle disappears after ovulation. The determination of basal body temperature is based on the change of hormone level. The level of progesterone increases during ovulation, and progesterone has a thermogenic effect, causing the body temperature to rise after ovulation.