However, in some cases, prenatal ultrasound can miss some fetal abnormalities. On average, one third to one half of fetal structural birth defects are not detected with ultrasound. Less commonly, ultrasound can sometimes indicate a fetal abnormality when no abnormality is present, causing stress and worry among the parents. A number of studies have shown that ultrasound is most effective when performed by an experienced physician at a major medical center. If ultrasound is needed very early during pregnancy, transvaginal ultrasound, rather than transabdominal ultrasound, is typically performed.
Transvaginal ultrasound is performed by inserting a probe into the vagina.
Early during pregnancy, the probe is able to get close to the uterus and is helpful in visualizing the fetus. As the pregnancy progresses, transabdominal ultrasound becomes more beneficial than transvaginal ultrasound. Transabdominal prenatal ultrasound is used to check on the development of the fetus and look for abnormalities. A special type of ultrasound exam called echocardiography images the blood flow through fetal heart chambers and major blood vessels to help detect heart irregularities. Ultrasound image of umbilical cord.