NT is NT examination and 4D is 4D color ultrasound. NT examination and 4D color ultrasound both belong to the examination to understand whether the fetus is healthy or not, the methods and purposes of these two examinations are different, and the main differences between them are as follows: 1. It is mainly to check whether the fetus has abnormal development of each organ. 4D ultrasound presents clearer images and can observe the dynamic images of each organ, which can exclude fetal brain, lung, intestine and spine malformations, and also can exclude limbs and facial malformations, such as cleft lip and palate. Different examination time: 1, NT examination: NT examination is conducted at 11-13 weeks of pregnancy, pregnant women can go to the hospital for examination during this period; 2, 4D ultrasound: 24-28 weeks of pregnancy is the best time to take 4D ultrasound, because the brain of the fetus enters the developmental stage around 24 weeks, at this time, the structure of the fetus, liver, gallbladder, pancreas, spleen, kidney and other organs are basically formed, the size of the fetus is moderate, the amniotic fluid is also moderate, and there is more room for movement in the uterine cavity, so the images are more likely to be seen. The fetus is of moderate size, the amniotic fluid is also moderate, and the space for activity in the uterine cavity is relatively large and the images are clearer. The NT examination is an ultrasound examination and does not require fasting. The fetus is too small to be detected and too large will also affect the detection result. It is not necessary for pregnant women to have an empty stomach to do 4D ultrasound. The pregnant woman must have a good rest the night before the 4D ultrasound to ensure that she has plenty of energy for the next day’s delivery.