Prenatal ultrasound examination with two-dimensional ultrasound is sufficient, if there is a special need, you can do four-dimensional ultrasound to help diagnose, there is no need for every pregnant woman to do four-dimensional ultrasound. Obstetric ultrasound is divided into primary, secondary and tertiary prenatal ultrasound and targeted examinations, and the usual tertiary ultrasound examination is the tertiary ultrasound examination. If the fetus has special conditions that cannot be diagnosed at the end of the tertiary ultrasound examination, 4D ultrasound can be performed according to the specific situation. 4D ultrasound can help the ultrasonographer diagnose some diseases that cannot be diagnosed with 2D ultrasound, which is limited to a small number of cases, for example, when some structures in the posterior cranial fossa pool are not clearly visible in the fetus’ skull, it is difficult for the doctor to make a section that can help diagnose the disease due to the limitation of the fetal position when using 2D ultrasound alone. In this case, 4D ultrasound can assist the ultrasonographer to see certain structures in the cranial fossa clearly and facilitate further diagnosis. For example, 4D ultrasound of the heart can show each section in more detail and help the ultrasonographer to diagnose certain diseases. However, 4D ultrasound is more troublesome and time-consuming than 2D ultrasound. In the absence of special circumstances, 2D ultrasound is sufficient for obstetric ultrasound.