1, a sentence to tell you the difference between one-dimensional, two-dimensional, three-dimensional, four-dimensional ultrasound Ultrasound began with the A-type ultrasound diagnostic method, that is, one-dimensional ultrasound, popularized in China in the early 60s, it only shows the echo amplitude of different tissues, no visual imaging of organs. The emergence of B-type ultrasound diagnostic method, i.e., two-dimensional ultrasound, replaced A-type ultrasound in the 1970s. To date, two-dimensional ultrasound is still the main method of ultrasound diagnosis. The three-dimensional ultrasound technology that everyone is concerned about is based on two-dimensional ultrasound for imaging, which must be combined with two-dimensional ultrasound or reconstructed by computer using images from two-dimensional ultrasound. Therefore, the quality of two-dimensional images directly affects the effect of three-dimensional imaging. Similarly, four-dimensional ultrasound is based on three-dimensional ultrasound to increase the time axis, that is, dynamic three-dimensional imaging, so it is also inseparable from the two-dimensional ultrasound. 2, the fetus large malformation ultrasound screening need three-dimensional or four-dimensional ultrasound? The first thing pregnant mothers should understand is that the purpose of prenatal ultrasound is to find out if there are structural malformations in the fetus, not to see what the baby looks like. The correct rate of prenatal diagnosis is affected by the level of the doctor, the week of pregnancy, the amount of amniotic fluid, the thickness of the pregnant woman’s abdominal wall, the type of fetal malformation, the position of the fetus, the time spent on the examination and many other factors, in addition to the requirements of the ultrasound equipment. It is not clear that 3D or 4D is better than 2D as we all understand. For example, when a fetal cleft lip is detected by 2D ultrasound, 3D ultrasound imaging can be used to obtain a 3D image of the fetal lip so that the pregnant woman and her family can understand it more visually. However, the primary condition for 3D ultrasound to be used for fetal examination is that the 2D images are clearly displayed and the fetal position is highly compatible. If the fetal position is not good or the fetus moves more when doing 3D imaging, 3D imaging will show some artifacts. 3.When can 3D and 4D ultrasound be used? The 3D and 4D ultrasound examinations currently carried out include the diagnosis of uterine malformations, detection of ovarian volume and follicles in polycystic ovary syndrome, fetal high-risk ultrasound, and fetal heart ultrasound. These examinations all serve as an adjunctive diagnostic role to conventional 2D ultrasound and do not replace 2D ultrasound. All patients or pregnant women must first undergo 3D or 4D imaging on the basis of the diagnosis of 2D ultrasound.