Proper ultrasonography is important for the early identification of fetal birth defects and for prenatal intervention. Of course, this also depends on the quality control of ultrasound examination. The following is the number of ultrasound examinations recommended by the Obstetrics and Gynecology Group of the Chinese Society of Obstetrics and Gynecology (February 2011), the original text is as follows: the recommended number of 4 to 5 times are 6 to 13 weeks +6, 18 to 24 weeks, 30 to 32 weeks and 37 to 41 weeks, respectively. thickness (NT), 18 to 24 weeks for systematic ultrasound screening for fetal malformations, 30 to 32 weeks to assess fetal development, and 37 to 41 weeks to determine amniotic fluid volume, placenta and fetal development. First: 6 to 9 weeks of pregnancy: to determine intrauterine pregnancy and also to help determine the number of weeks of pregnancy in pregnant women with irregular menstruation; Second: 11 to 13+6 weeks of pregnancy: fetal posterior nuchal translucency thickness, or NT screening, is an important ultrasound indicator for Down’s syndrome screening stage I. Third: 22 to 28 weeks of pregnancy, preferably 25 to 26 weeks, 3D ultrasound screening, many hospitals require an appointment 3 to 4 weeks in advance, including our hospital. The fourth: 31 to 32 weeks of pregnancy, to understand the fetal position, fetal development, amniotic fluid and placenta, which can detect early problems such as fetal growth restriction and abnormal amniotic fluid volume. Routine prenatal checkups, i.e. measuring uterine height, abdominal circumference, checking fetal position, listening to fetal heartbeat and fetal heartbeat monitoring, are unable to know exactly these intrauterine conditions. Fifth: 37 to 41 weeks of gestation, prenatal assessment of fetal size, amniotic fluid, etc. This examination cannot be omitted, especially for high-risk pregnancies such as gestational diabetes, intrahepatic cholestasis syndrome during pregnancy, and scarred uterus. Even if it is not done in the outpatient clinic, it should be checked after admission to the hospital. If we know the situation earlier, we can deal with it in time to avoid delaying the best time for delivery and the occurrence of giant fetus, low amniotic fluid, intrauterine distress, etc. Of course, if the situation is special, such as pre-eclampsia, abnormal placental position, fetal development, etc., the number of examinations will be increased according to the specific circumstances, in general, doing ultrasound is not harmful to the fetus, but of course, the number of examinations should not be increased indiscriminately without necessity.