The best time for a 4D ultrasound during pregnancy is between 20-24 weeks as recommended by the current pregnancy healthcare guidelines, although it will vary for each individual pregnant woman. At 20-24 weeks of pregnancy, the fetus’ limbs and major organs are mature, and the size of the fetus and the pregnant woman’s own amniotic fluid volume are more suitable for a 4-D ultrasound to get clearer pictures. The examination can clearly see the development of the fetus, and can more accurately determine whether the fetus has congenital developmental abnormalities, such as cleft lip and palate, microcephaly, spina bifida, etc. Moreover, it is able to make an assessment of the amniotic fluid volume, the fetus’s femur length, and the biparietal diameter, so as to determine whether the fetus is in line with the week of pregnancy. Before 20 weeks, the fetal body organs may not be mature, the examination results may be inaccurate; after 28 weeks due to the fetal development is too large, the amniotic fluid decreases, resulting in reduced fetal activity, easy to cause missed diagnosis, so it is recommended that pregnant women in the appropriate week of pregnancy for 4D examination.