The best time to have a 4D examination is between 22 and 26 weeks, which is the best time period. This is because at this time, the fetus has been fully developed, the size of the fetus and the amount of amniotic fluid is just right, and the skeletal echoes will be less affected, so the examination images will be clearer and the possibility of malformations can be ruled out. For facial deformities, digestive system, urinary system, brain development, heart development, can make accurate judgments, can determine whether the fetus has malformations, this belongs to the best way to achieve eugenics during a test. If there is a fetal malformation, it is possible to avoid having a malformed child born.