A vaginal ultrasound (vaginal ultrasound) is an ultrasound performed by inserting a long probe deep into the vagina. Some pregnant women think that vaginal bleeding will occur after a vaginal ultrasound and that this will cause an increased risk of miscarriage. This is not the case. The small amount of vaginal bleeding is caused by irritation of the cervix during the examination and is not bleeding from inside the uterine cavity. Unlike X-rays and CTs, there is no ionizing or electromagnetic radiation, so there is little or no harm to the human body, and there have been no definitive studies on the adverse effects of diagnostic ultrasound on the embryo or fetus. It is the same as abdominal ultrasound, except that the probe is placed in a different position and the doctor changes the condom on the probe for each patient examined, without increasing the risk of infection. Benefits of vaginal ultrasound: no need to hold urine, can see the gestational sac earlier, clarify whether it is intrauterine or extrauterine (transabdominal ultrasound can only be seen at 5-6 weeks after menopause, vaginal ultrasound can be seen at 4 weeks after menopause), and can more clearly distinguish whether there is any abnormality of the uterus and ovary, such as deformity or tumor. Vaginal ultrasound should be performed in the following cases: abnormal bleeding and abdominal pain (for earlier diagnosis and treatment), previous cesarean section and second pregnancy (6-7 weeks of vaginal ultrasound can clarify the distance between the gestational sac and the uterine scar, to rule out keloidal pregnancy), suspected cervical insufficiency (cervical length changes are monitored continuously at 2-week intervals from the 14th-16th week of pregnancy), suspected placental abnormality (the abdomen is difficult to visualize the placenta and the uterus at late stages of pregnancy), and suspected abnormalities (the placenta and the uterus can not be seen at all during late pregnancy). (late pregnancy abdominal ultrasound is difficult to see the relationship between the placenta and the endocervical opening, yin ultrasound can be very good to clarify the placenta praevia, umbilical cord preexposure, anterior vascular and other dangerous situations), maternal obesity (abdominal fat is too thick, abdominal ultrasound can not be seen). Yin ultrasound is an upgraded version of conventional ultrasound in obstetrics and gynecology, and doing it in the early stages of pregnancy has no obvious harmful effects on the embryo; on the contrary, it can assist in clinical diagnosis earlier and better.