The 4D ultrasound is done in the middle of the pregnancy, and usually does not require fasting. This period is the most important malformation screening period in the whole pregnancy, so the examination items are more, the examination time is relatively long, and even some times because of the influence of the fetal position, need to move the mother-to-be and then carry out the examination. So if you need to take a checkup, you can bring some snacks or fruits with you. Four-dimensional examination needs to take pictures, usually take pictures of the face of the fetus, want to take a better picture of the face, need to be very good with the fetus. In some clinical cases, after some pregnant women eat sweeter food, the baby will change its position and finish the examination smoothly. Four-dimensional examination of the examination position is variable, generally lying position and lateral position, because the examination time is relatively long, when the mother-to-be lying time is longer, there is uncomfortable feeling, must promptly communicate with the examining doctor, at this time should stop the examination or change the position to rest. When the ultrasound doctor suspects that the position of the placenta is low, it is necessary for the mother-to-be to hold her urine and then carry out the examination. Generally, you need to drink 500ml of water for half an hour and then carry out the examination, so that the error of the examination will be smaller. So it is not necessary to do four-dimensional ultrasound on an empty stomach.