4D color ultrasound can be done in the afternoon, and there is no strict time limit. As a clinical detoxification tool, 4D color ultrasound is recommended to be performed at 20-24 weeks of pregnancy, too early to check the observation is not clear, too late to check the fetus is too big, it may not be observed clearly, and because the fetus is too big, if abnormalities are found, it is difficult to deal with them at this time. 4D ultrasound can observe the fetal growth and development in the womb in a multi-directional, multi-angle and dynamic way, and provide scientific basis for early diagnosis of fetal congenital anomalies and congenital heart diseases, and the anomalies that can be diagnosed mainly include the following: 1) facial anomalies: such as cleft lip and cleft palate; 2) nervous system: anencephaly, hydrocephalus, microcephaly, spina bifida and cerebrospinal membrane bulge; 3) digestive system: umbilical bulge 4.Urological system: hydronephrosis, polycystic kidney and giant bladder, urethral obstruction; 5.Other malformations: short limb malformation, joint malformation, cleft lip, four heart cavities. Besides observing whether the fetus has malformations, 4D ultrasound can also clarify whether the amniotic fluid is too much or too little. Before the 4D ultrasound examination, pregnant women can move or eat appropriately to stimulate intrauterine movement of the fetus and facilitate observation of fetal structures. For pregnant women with suspected fetal heart valve movement abnormalities, 4D ultrasound observation is more advantageous.