A vaginal ultrasound is not recommended on the last day of menstruation. The last day of menstruation mostly means that the menstruation has not yet ended. When the menstruation has not yet ended, there will be bleeding in the vagina, and doing an ultrasound in this case may increase the chances of infection, and may even have an effect on the results of the examination. Therefore, it is recommended to do the ultrasound 2~3 days after the menstruation completely stops, it is better to do the ultrasound. However, there are certain precautions to be taken when having a vaginal ultrasound examination, such as: pay attention to avoiding sexual intercourse, avoiding menstruation, emptying the bladder, and so on. Ultrasound of the uterine cavity and the pelvis can be more clearly observed, compared with the transabdominal ultrasound is more clear. However, on the last day of menstruation, when you want to do ultrasound examination, it is recommended to use transabdominal ultrasound.