The major screening program mainly refers to the obstetric systematic ultrasound examination, which provides a comprehensive examination and evaluation of the growth of the fetus, the development of various organs and appendages. Obstetric systematic ultrasound is usually performed once in the 22nd to 24th week of pregnancy and once in the 28th to 30th week of pregnancy to measure the head circumference, abdominal circumference, femur length, and other radii of the fetus, and to assess whether the growth is in accordance with the week of pregnancy. At the same time, systematic ultrasound provides comprehensive morphological screening of all fetal organ systems, including the limbs and bones, the digestive system, the urinary system, and the facial features, to assess the presence of malformations or certain disorders in the fetus for early intervention. Systematic ultrasound also routinely examines fetal appendages, including the umbilical cord, amniotic fluid, placenta, etc. If there is any abnormality, the doctor will take appropriate measures to deal with it.