A grand mal is a test that needs to be done for pregnant women within a certain period of time. 4D ultrasound is a screening test for pregnant women between 20 and 24 weeks of pregnancy, so 4D ultrasound is a type of grand mal. The usual ultrasound for routine checkups is two-dimensional ultrasound or three-dimensional ultrasound, therefore, the biggest difference between them is the difference of the machines. In addition, in terms of imaging, ordinary ultrasound is two-dimensional or three-dimensional imaging, while 4D ultrasound is a three-dimensional image, and it is a real-time dynamic image. Therefore, 4D ultrasound has better visualization, clearer images, and higher accuracy rate of malformations that can be detected. Major abnormality can show the color of the fetus, the face, the development of each organ, and even observe the state of the fetus in the mother’s body. Early diagnosis of fetal abnormalities such as cleft lip, cleft palate, abnormal bone development, cardiovascular abnormality, digestive system abnormality, and urinary system abnormality can be made. Its technology has been quite perfect, and it can completely detect larger malformations of the fetus, but the tiny five senses such as the shape of fingers, toes and ears are not included in the screening. The 4D ultrasound, on the other hand, shows more clearly on the image and can record the dynamic picture of the fetal baby in the mother’s womb, which can provide accurate scientific basis for the early diagnosis of fetal congenital body surface anomalies and congenital complex anomalies. At the same time, it can clearly show fetal polycystic kidney and renal dysplasia, and has important value in determining fetal congenital heart disease.