It is best to do 4D ultrasound at 20-24 weeks of pregnancy, which varies slightly from hospital to hospital. At 20-24 weeks of pregnancy, the fetus’ limbs and all major organs are fully developed, and the amniotic fluid volume is sufficient, so it is easier to collect relatively clear images, which can clearly show whether the baby in the body has the presence of cleft lip, cleft palate, abnormal bone development, cardiovascular malformations and other anomalies. If the 4D ultrasound is performed at an early stage, the fetus is still small at this time and does not achieve satisfactory screening conditions. If the four-dimensional ultrasound screening in the late pregnancy, due to the larger fetus, intrauterine amniotic fluid is less, see the fetus in the abdomen and physical development is not very clear, but can observe the shape of a certain part of the fetus. It is recommended that you choose a regular hospital to make an appointment in advance for the 4D ultrasound and follow the doctor’s instructions for the time of the examination.