Vaginal ultrasound is relatively not recommended at this time of the month because of decreased resistance due to vaginal bleeding. However, in some special cases, clinicians may recommend vaginal ultrasound when menstruation has just started and there is a little vaginal bleeding, including the following two aspects: First, patients who think that this bleeding is menstruation, but in fact it is abnormal uterine bleeding, may have vaginal ultrasound when the bleeding has just started and there is not much vaginal bleeding. Secondly, among assisted reproductive techniques, the reproductive physician will advise the patient to go for a vaginal ultrasound at the beginning of the period to monitor the number of sinus follicles and thus understand ovarian function. Therefore, vaginal ultrasound can be done in cases of a little vaginal bleeding or when the vaginal bleeding is not significant at the beginning of the menstrual period, given the clinical diagnosis and the relatively low chance of vaginal infection.