With the advancement of science, 4D ultrasound has become an indispensable examination tool for people after pregnancy. Compared to traditional ultrasound, 4D ultrasound shows the surface of the fetus more clearly and accurately, and can reveal real-time dynamic images of the unborn baby’s activities. The examination time of 4D ultrasound also varies from person to person and can be determined according to individual needs. For example, before 12 weeks of pregnancy, 4D ultrasound is generally not recommended for safety reasons. After 16 weeks of pregnancy, the baby’s limbs and main organs are mature, and the amount of amniotic fluid at this time is also relatively large, which is suitable for the baby to move around in the womb and facilitate more intuitive detection of the baby’s development, so between 16 and 24 weeks is the best time to do 4D ultrasound to detect the baby’s development. In order to exclude the baby’s external defects, 4D ultrasound can also be done in late pregnancy to observe the shape of a certain part of the baby. To sum up, the time of 4D ultrasound examination during pregnancy needs to be determined according to the specific situation. 4D ultrasound can visually observe the baby’s appearance and limb development, and can promptly detect subtle developmental abnormalities that exist in the fetus.