Pregnant women have Down’s syndrome screening in the fourth month of pregnancy, mainly to screen the possibility of the fetus having Down’s syndrome. The passing rate of 4D ultrasound is generally above 80%, but it is not because of the passing of Down’s screening that the 4D passing occurs, but because the 4D ultrasound is mainly to check for malformations of the fetal parenchymal organs, and the vast majority of them are normal fetuses, so the passing rate is relatively high. Only a small number of fetuses may not pass the 4D due to their own organ malformations or other chromosomal abnormalities. If the 4D cannot be passed, direct amniocentesis will usually be considered to further rule out chromosomal abnormalities.