Improving the quality of population and controlling the quality of population is an important national policy of family planning in China. Reducing the birth of defective children and having a healthy baby are the concerns of every family and the whole society, and the direction that all workers engaged in perinatal health care are striving for. Ultrasound diagnosis has been widely used in prenatal fetal monitoring work because it is non-invasive, non-radiographic, safe, convenient and can dynamically observe the structure of each fetal organ, and is one of the important prenatal diagnostic imaging means. What problems might ultrasound solve for your baby when you are pregnant? When is the most appropriate time to have an ultrasound examination? We recommend that you have at least 3-4 fetal ultrasound exams when you are pregnant with your baby. 1.Early pregnancy ultrasound at 10-14 weeks; mainly for gestational age assessment and NT measurement. 2.20-26 weeks of gestation ultrasound; mainly for systematic screening of fetal structural malformations. 3.Ultrasound examination at 28-32 weeks of gestation; mainly to understand the fetal growth and development, whether the placenta, umbilical cord and amniotic fluid are normal and further screening of fetal structural malformations. 4.Ultrasound examination before birth to prepare for smooth delivery. Systematic fetal ultrasonography and 3D and 4D ultrasonography These are two different concepts, the former refers to a type of prenatal ultrasonography, the latter is the two imaging methods used in prenatal ultrasonography, at present a considerable number of pregnant women and their families are prone to confuse the two. There are four types of prenatal ultrasound examination regulated by the prenatal diagnosis expert group of the Ministry of Health, namely: (1) early pregnancy ultrasound examination. (2) Routine ultrasonography in middle and late pregnancy. (3) Systematic ultrasonography in mid- to late-term pregnancy. (4) Targeted ultrasound. Each type of ultrasound examination is aimed at different conditions of pregnant women, and the requirements of the examination are also different. Among them, the system ultrasound examination for mid- and late-term pregnancy is mainly to screen for fetal structural malformations, which is also commonly known as “teratology examination”, and many members of the public mistake this examination for 3D-4D ultrasound examination. It can be used in any of the above four types of ultrasound examinations, including gynecological uterine examinations. 2D ultrasound is the basis of 3D 4D ultrasound, based on which 3D 4D ultrasound can provide more diagnostic information, such as for surface imaging of the fetus, such as taking pictures, etc. Certain planes that cannot be shown by 2D imaging can be obtained by 3D imaging, which can be helpful for diagnosis. However, 3D-4D ultrasound has higher requirements for the position of the fetus in the uterus, the amount of amniotic fluid, and the thickness of the abdominal wall of the pregnant woman, so the main diagnostic work is still done by 2D ultrasound. Although prenatal ultrasound can diagnose most fetal structural malformations, ultrasound still has its limitations. Even with the best equipment and the best sonographers, it is still not possible to diagnose all fetal anomalies, such as malformations of the fingers and toes, abnormalities in the shape and position of the ear, and simple atrial septal defects and ventricular septal defects of the heart. Ultrasound cannot diagnose functional abnormalities such as cerebral palsy, mental retardation, visual impairment, hearing impairment, and metabolic disorders.