4D ultrasound, also known as fetal system structure screening, mainly screens for malformations in the development of various fetal organs, and the best time for screening is between 22 and 28 weeks of pregnancy. The best time for screening is between 22 and 28 weeks of pregnancy. 4D ultrasound requires high technical level of doctors, and not every hospital is qualified to carry out 4D ultrasound examination. During the 4D ultrasound examination, you do not need to have an empty stomach, you can have the examination after having breakfast. After eating, the fetus is more active, which is beneficial for the doctor to conduct a comprehensive examination of the fetus. If one examination is unsuccessful, the pregnant woman can be allowed to repeat the examination again after being active. In addition, even if the 4D examination is normal, the possibility of fetal developmental abnormalities cannot be completely ruled out because some of the fetal organs are not fully developed at the time of the 4D examination. Between 30 and 32 weeks of pregnancy, fetal system structure examination is still needed to rule out fetal hydrocephalus and heart malformations.