When performing the 4D ultrasound examination, if the fetus is less active and in an incorrect position, the pregnant woman can be instructed to take a walk for about 15 minutes or try to perform the 4D examination in the afternoon. The fetus starts to move consciously at 20 weeks of pregnancy and the prenatal 4D examination is performed at 24 weeks of pregnancy. Because the activities and emotional changes of pregnant women will cause some stimulation to the fetus, so when the fetus is inactive, pregnant women can be instructed to strengthen the activities, such as walking for 15 minutes, but should pay attention to the intensity of exercise and exercise safety. Fetal movement will disappear when the fetus is in sleep cycle, at this time, the fetal position is fixed, it is difficult to obtain the fetal position required by the four-dimensional examination. Fetal movement is generally more active at night and in the afternoon. It is recommended to make an appointment for an afternoon 4D examination when fetal movement is active.