Nowadays, 4D ultrasound is routinely done after pregnancy, usually between 22-24 weeks. 4D ultrasound is an image generated at a later stage, not the image observed is 4-dimensional, it still relies on the ordinary ultrasound observation, and then through the conversion software in the instrument, the observed flat image is transformed into a 4-dimensional three-dimensional image. In the sense of diagnosis, three-dimensional ultrasound and four-dimensional ultrasound do not have any more advantageous place for diagnosis, except that people who do not know ultrasound images are also able to see the model, and this is the advanced place of four-dimensional ultrasound. 4D ultrasound is video, which allows pregnant mothers to see a series of fetal movements. 4D ultrasound is dynamic and can burn CDs, which can show a series of fetal movements in the womb in high definition.