A pregnant woman should have at least five ultrasounds from the beginning of her pregnancy until she gives birth. The first examination should be chosen around 35-45 days of pregnancy to determine whether the pregnancy has been conceived, the location of the bed, and also to understand the number of embryos and their growth; the second examination is chosen between the 11th and 13th+6th weeks of pregnancy, which is the best time period to perform an early NT examination and screen for severe structural malformations in the early pregnancy, as well as to understand the basic development of the fetus; the third time is between the 18th and 24th weeks of pregnancy Detailed and systematic screening for fetal anomalies is performed during this period, which is the best time to screen for fetal anomalies; the fourth time is between 30-32 weeks to monitor fetal development, measure fetal size and further detect major anomalies; the final test should be chosen around 36-37 weeks of pregnancy to reassess fetal growth and development, and to determine the mode of delivery in preparation for the birth of the child.