Ultrasound can be performed at any time at the end of the menstrual period, i.e. when there is no vaginal bleeding, only that the uterus or ovaries are different at different times during menstruation. This is because the uterus and ovaries can undergo cyclic changes as the menstrual cycle changes. After menstruation, the endometrium will gradually become thicker and after ovulation, the endometrium can change morphologically due to the influence of progesterone. Therefore, the endometrium seen at different times after clean menstruation is different, including the ovaries as well. After menstruation, the ovaries can gradually increase in size, with the dominant follicle becoming larger and larger and becoming a mature follicle for ovulation at 14-15 days. After ovulation, the corpus luteum is formed and gradually turns into a white body. Therefore, during the course of the menstrual cycle, ultrasound examinations will reveal endometrial changes and ovarian changes, which change with the menstrual cycle and can be done in every period. In principle, negative ultrasound is not performed during menstruation, because vaginal ultrasound may cause the possibility of infection to exist when there is vaginal bleeding during menstruation. However, to evaluate ovarian function, to see if there are many polycystic follicles in the ovaries, as well as to see if pregnancy can occur normally, if the follicles will grow normally, and if the ovaries are functioning well, vaginal ultrasound is usually done on the second or third day of menstruation, or as medically necessary. If there is no medical need, a vaginal ultrasound is usually done after the menstrual period is well cleared.