The best time to have a 4D ultrasound is between 22-28 weeks of pregnancy. Because 4D ultrasound needs to be examined in a tertiary hospital, and it takes longer to do 4D ultrasound, about 40-60 min. the best time to do 4D ultrasound is between 22-28 weeks of gestation, if it exceeds this time period, the development of the fetus can not be well observed. Four-dimensional ultrasound is an important screening program during pregnancy by dynamically observing the fetal head, limbs, internal organs, especially the heart development for malformations while the fetus is moving in the uterus. It is best to wear loose, easy to put on and take off shoes and clothes for the 4D ultrasound, and to bring a small snack. During the procedure, if the fetus is in an inappropriate position, you can go out and move around for a while or eat a snack to induce fetal movement.