Fetal umbilical blood flow monitoring is a special test during pregnancy to assess the functional status of the placenta and the fetal blood supply and to predict the presence of intrauterine hypoxia by measuring the S/D value of fetal umbilical blood flow. If the S/D value of fetal umbilical cord blood flow increases during the monitoring of umbilical cord blood flow, it indicates that the blood supply to the placenta is impaired and the fetus may be hypoxic in the uterine cavity. If this state persists for a long time, it may lead to intrauterine growth retardation and a significantly poor prognosis for the child after birth.