The ultrasound for the screening is not necessarily a 4-dimensional ultrasound. The three-dimensional ultrasound examination can not only check the malformation of the fetal body, such as cleft lip and palate, spina bifida, limb malformation, but also the three-dimensional ultrasound can observe the fetal heart and whether there are developmental malformations in the gastrointestinal tract, which can be checked and confirmed. The fourth dimensional ultrasound is based on the three-dimensional ultrasound plus the fourth dimensional time dynamic examination, which can not only show the development of the fetal face and organs but also the state of the fetus in the mother’s body, and can diagnose fetal developmental abnormalities and cardiovascular malformations at an early stage. The first ultrasound screening is performed at 22-26 weeks and the second at 30-32 weeks, and it also includes early and mid-term Down’s syndrome screening.