Whether or not to perform a transvaginal ultrasound during a threatened miscarriage mainly depends on the symptoms of the threatened miscarriage. A threatened miscarriage refers to the signs of a potential miscarriage, with common symptoms including vaginal bleeding and severe abdominal pain. If there is significant abdominal pain, a transvaginal ultrasound can be performed to determine the position of the gestational sac, or an abdominal ultrasound can also be done. If there is vaginal bleeding, performing a transvaginal ultrasound in this case may aggravate stimulation to the uterus and can easily lead to vaginal inflammation. In such cases, an abdominal ultrasound is generally recommended. Therefore, a transvaginal ultrasound can be performed if there is only abdominal pain during a threatened miscarriage, but it should not be done if there is concurrent vaginal bleeding.