If the color ultrasound examination exceeds the time of half an hour, it may affect the development of the fetal retina. Normally color ultrasound examination has no effect on the fetus, ultrasound is not harmful to the body. However, if the ultrasound examination exceeds half an hour, the thermal effect of ultrasound may affect the development of the retina of the fetus, and the fetus may be born with amblyopia and so on. For the healthy development of the fetus, it is recommended that the duration of each fetal ultrasound examination should not exceed half an hour. When taking measurements, take the probe down and avoid prolonged contact. Whether the color ultrasound examination will affect the retina is related to the duration of the ultrasound examination, so the duration of the ultrasound examination, especially the 4D ultrasound, is recommended not to exceed half an hour.