In Canada, the birth rate of babies with fetal growth restriction is approximately 3.7%. It is estimated that around 60% of pregnancies complicated by fetal growth restriction are due to placental insufficiency. This insufficiency is characterized by an increase in placental vascular resistance combined with a decrease in umbilical blood flow. The oxygen delivery to the fetus is then reduced. Available tools actually used are not accurate enough to identify the ideal point in time for a preterm delivery in order to reduce the risks of brain damage related to hypoxia. Using ultrasound techniques (Doppler velocimetry), blood flow can be measured in fetal circulation including that of the placenta. By detecting changes in flow in a specific portion of the aorta called “the aortic isthmus (AoI)”, the present study aims at identifying a precise marker, the isthmus flow index (IFI), with which the risk of irreversible brain injury due to lack of oxygen can be evaluated. We had previously observed, with a limited number of subjects, that fetuses with growth restriction and an IFI below 0.7 presented a high rate of anomalies during neurological assessment between ages 2 and 5 years. The aim of this study is to validate, based on a greater number of fetuses, the IFI threshold below which the risk of cerebral hypoxia would justify a preterm delivery.