4D ultrasound is recommended to be done between 22-26 weeks after pregnancy, which is equivalent to 5-6 months of pregnancy. During this period, the fetus has been fully developed, and all the limbs, head and internal organs have been developed, and the fetal body size is suitable and the amniotic fluid volume is moderate, which is more conducive to fetal movement and can clearly display the fetal structure and help to detect certain parts of the fetus, such as anencephaly, spina bifida, heart malformation, cleft lip and palate, and physical disabilities. 4D ultrasound is also a very critical clinical examination during pregnancy. Since 4D ultrasound examination takes a long time, it is recommended to make an appointment in advance. 4D ultrasound is also the most advanced ultrasound in the world at present, which is based on the three-dimensional ultrasound stereoscopic reconstruction and adds the concept of time, which can provide real-time dynamic pictures of the fetus.