Four-dimensional ultrasound is the most important prenatal examination for fetal malformation during the whole pregnancy, and compared with other ultrasound examinations during pregnancy, four-dimensional ultrasound examination has more items and is more comprehensive and detailed. Clinically, during the 4D ultrasound examination, due to the influence of the mother and the position of the fetus and other factors, it is often not possible to complete the examination at one time, so it is necessary to stimulate the fetus to change the position and carry out the examination again. Some pregnant women even need more times to complete the 4D ultrasound examination. During the four-dimensional examination, when the position of the fetus is not suitable for observing the section of the organs to be explored, such as the limbs of the fetus blocking the face, some ultrasound doctors will use the probe to push from the side of the pregnant woman’s abdomen to stimulate the fetus, so that the limbs of the fetus will be lifted up to show the purpose of the face. But when the fetus is resting, this stimulation is ineffective. And because the 4D examination time is relatively long, pregnant women will feel tired after lying down for a long time, the doctor usually suggests pregnant women to go outside activities such as through walking, or climbing stairs and other ways to stimulate the fetus to move. In addition, the sensitivity of the fetus to different stimuli is not the same. In some cases, the position of the fetus changes when the mother eats sweet foods such as sugar or chocolate. Most of these stimuli are only relative changes in the position of the fetus, and it is not easy to really stimulate the fetus to roll over.