The venous catheter is connected between the umbilical vein and the inferior vena cava, which is vital to the blood circulation of the fetus, and can provide oxygen to the fetus to promote its growth and development, and it can also be used to determine the development of the fetus and the early detection of developmental abnormalities through the ultrasonography of the venous catheter and the detection of the venous catheter blood flow, and therefore it is of great significance to the fetus: 1. Promoting development: the venous catheter is a vein produced during the fetal period for connecting with the liver The venous catheter is a vein created during fetal life to connect to the liver, and it can pass the blood from the placenta into the inferior vena cava through the venous catheter, and then into the right atrium, thus providing abundant oxygen to the fetus to meet the needs of its growth and development; 2. Monitoring the development of malformations: ultrasonography of the venous catheter is an important ultrasound indicator to monitor the existence of abnormalities in the early stage of the fetus. The venous catheter is connected between the umbilical vein and the inferior vena cava, a vein with a narrow inlet and a wide outlet, and is a major vein in the fetal circulation. If the spectrum of fetal venous catheter shows abnormality, it means that the fetus may have the risk of abnormality, which is mainly manifested as chromosomal abnormality and congenital heart disease; 3. Judgement of fetal development: Through venous catheterization blood flow test, it can provide a reference basis to understand the intrauterine safety and danger of the fetus in the middle and late pregnancy in order to determine the time to terminate the pregnancy.