Abstract: The lack of oxygen in uterus puts a severe threat to the fetus，so obstetricians have paid great attention to the issue for rather a long time. The early discovery of epidemics and timely treatment are of great significance to decrease of the death rate of new-born babies and improve perinatology. At present，the color Doppler ultrasound method is used to measure the index of the fetal umbilical artery and the blood flow in the middle cerebral artery so as to evaluate the situation of the lack of oxygen in the uterus. The article aims to disuss the significance of Dopper ultrasound in measuring the aortic isthmus of fetus in an easy， convenient， fast and effective way.

Key words: Fetal hypoxia, Ultrasonography, Doppler, Aorta, Fetal growth retardation, Fetal monitoring