A 4D mini-exam at 30 weeks of pregnancy is usually mandatory. The second xenography during 28-30 weeks of pregnancy, also known as the minor xenography, is one of the important items of the maternity checkup and is usually mandatory. Its main purpose is to determine whether there is any developmental abnormality of the fetus in the late stage of pregnancy through ultrasonography, and at the same time to understand the condition of the amniotic fluid and the placenta, to determine whether there is any umbilical cord circumference of the fetus, and to assess the safety and danger of the fetus through the umbilical cord blood flow. Mini-detectorial ultrasound through the four-dimensional ultrasound on the nervous system, cardiovascular system, genitourinary system, digestive system, etc. to carry out a comprehensive examination, can be found in the abnormal development of the fetus, congenital anomalies, such as tetralogy of Fallot, spina bifida, open neural tube malformations, etc., the timely detection of anomalies can be considered as early as possible termination of pregnancy, in order to avoid irreversible results. If the results of the micro-anomaly test during pregnancy are abnormal, it is recommended to seek medical attention in time, with the help of a doctor to clarify the diagnosis and timely intervention to avoid adverse consequences.