Nowadays, pregnant mothers undergo an ultrasound between 22-26 weeks of pregnancy. Is it better to choose 3D ultrasound or 4D ultrasound? In fact, the images of 3D and 4D ultrasound are generated at a later stage, and the images observed are not 3D or 4D, but are observed using ordinary ultrasound, and then the flat images observed are transformed into 3D and 4D stereoscopic images through the conversion software in the instrument. To put it more bluntly, it is the conversion of some ordinary ultrasound images into stereoscopic ones. Four-dimensional ultrasound is dynamic, three-dimensional ultrasound is static, so generally speaking, the equipment that can do three-dimensional ultrasound can do four-dimensional ultrasound, both images are the same. What we usually call three-dimensional is in fact a fetal system screening, which itself is performed in two dimensions and finally generates a three-dimensional image, so people call it smooth and equate the fetal system screening to three-dimensional.