4D ultrasound can be performed at 17 weeks of pregnancy, but the accuracy of the test results is low. 4D ultrasound is usually recommended at 20-28 weeks of pregnancy to rule out fetal malformations during pregnancy. 4D ultrasound is an advanced ultrasound examination technology that can screen the fetal face and cranial tissue for possible defects such as cleft lip and palate, hydrocephalus and microcephaly at an early stage, and can also assist in excluding limb malformations, spina bifida and pathologies that endanger fetal health such as congenital heart disease and hydronephrosis. Since the amniotic fluid is not particularly sufficient at 17 weeks and the fetus is not yet well developed, the 4D examination at this time cannot achieve good examination results and may be missed. After 20 weeks of pregnancy, the fetal brain develops rapidly, the fetal structure has been formed, and the amniotic fluid is sufficient, so the fetus has a relatively large space to move around in the uterine cavity, which makes it easy to obtain clear images, so that the fetal development can be observed more accurately, so pregnant women should accurately grasp the time of 4D ultrasound examination. In addition, Down’s syndrome screening can be performed at 17 weeks of pregnancy to determine the risk factor of fetal Down’s syndrome and neural tube defects, which is also important for monitoring fetal development during pregnancy.