4D ultrasound is usually done between 22-28 weeks of pregnancy, which is better because the fetus’ organs and facial structures are more developed at this time. The amount of amniotic fluid in this time period is more adequate, which is better for observing the fetus. The 4D ultrasound can diagnose many diseases, such as surface imaging, which can clearly see whether the fetus has facial deformities, cleft lip and cleft palate, etc.; in the neurological system, it can detect anencephaly, hydrocephalus, microcephaly, spina bifida and cerebrospinal membrane bulge; in the digestive system, it can reveal visceral ectopia, intestinal atresia, giant colon, etc.; in the urinary system, it can detect hydronephrosis, polycystic kidney, giant bladder, etc. In the urinary system, hydrocele, polycystic kidney, giant bladder, etc. can be detected; other limb deformities can also be detected.