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 also can determine the fetal development and early detection of developmental malformations through venous catheter ultrasonography and venous catheter blood flow detection, so it is of great significance to the fetus: 1, promoting development: the venous catheter is a vein created during fetal life to connect the liver The ductus venosus is a vein created during fetal life to connect to the liver, which allows blood from the placenta to enter the inferior vena cava through the ductus venosus and then the right atrium, thus providing the fetus with abundant oxygen to meet its growth and developmental needs; 2, monitoring the development of abnormalities: the ductus venosus ultrasonography is an important ultrasound indicator to monitor the presence of abnormalities in the early fetal life. The venous duct is connected between the umbilical vein and the inferior vena cava, a vein with a narrow entrance and a wide exit, and is a major vein in the fetal circulation. If the venous catheter spectrum shows abnormalities, it means that the fetus may be at risk for abnormalities, mainly chromosomal abnormalities and congenital heart disease; 3.