This kind of examination generally does not need special preparation before doing four-dimensional color Doppler ultrasound, and the flow of ordinary color Doppler ultrasound examination is basically the same. However, during pregnancy, four-dimensional color Doppler ultrasound is usually reserved in the middle and late stages of pregnancy. Four-dimensional color Doppler ultrasound screening for fetal structural development in the second trimester can find some abnormalities in fetal structural development, including neural tube development defects, anencephaly, hydrocephalus, chest and abdomen wall defects, limb deformities, severe cleft lip and palate, etc. Prenatal screening B-ultrasound is everywhere, and prenatal diagnosis is needed if there is abnormality.