The best time to have a 4D ultrasound is between 22 and 26 weeks of pregnancy, because the fetus is the right size and the amniotic fluid volume is moderate, and the fetal skeleton will not have a great impact on the 4D ultrasound. The ultrasound during this period can also accurately see whether there is congenital developmental defects, whether the face is normal, cleft lip and palate, congenital heart abnormalities, kidney abnormalities or intracranial developmental abnormalities can all be detected through 4D ultrasound. If the fetus has developmental abnormalities, those that are not serious can be treated by surgery or some other means after birth to allow it to live a normal life. However, if the fetal developmental abnormalities are particularly serious, such as cleft lip and palate, and cannot achieve a normal life through surgery after birth, such a fetus should not be allowed to be born, otherwise it will bring some pain and burden.