Two-dimensional ultrasound is the imaging of a section, three-dimensional ultrasound adds a representation of three-dimensional space to the two-dimensional image, and four-dimensional ultrasound adds a representation of the timeline to the three-dimensional one. Two-dimensional, three-dimensional, and four-dimensional space are descriptions used to define the dimensions of an ultrasound examination. The development of medical ultrasound technology has successively included A ultrasound, B ultrasound, M ultrasound, D ultrasound, three-dimensional ultrasound, four-dimensional ultrasound and so on. The commonly used clinical ultrasound examination has two-dimensional, three-dimensional and four-dimensional ultrasound, the difference is as follows: 1. 2D ultrasound: the image is only a two-dimensional image, which is a section of the imaging. 2. Three-dimensional ultrasound: the results are clearer, clearer, is a two-dimensional image based on three-dimensional space performance. 3. Four-dimensional ultrasound: ultrasound images are more dynamic, clear and three-dimensional, based on the three-dimensional ultrasound, but also added to the timeline of the performance. Ultrasound is often used to assist in checking whether the fetus has developmental malformations and other abnormalities, and it is recommended to conduct the corresponding examination under the guidance of a doctor.