The normal value of umbilical cord S/D decreases with the increase of gestational weeks, <5 before 30 weeks of gestation, <4 during 30-36 weeks of gestation, and <3 after 36 weeks of gestation.The higher S/D value reflects the poorer blood supply to the placental site, which is commonly seen in intrauterine distress, umbilical cord torsion, umbilical cord entanglement, intrauterine growth restriction of the fetus, placenta previa, and low amniotic fluid, etc. Once elevated S/D value is found, especially when there is no blood flow in the umbilical artery at end-diastole, the fetus may die within 1 week. Once the S/D value is found to be elevated, especially when there is no blood flow in the umbilical artery at the end-diastolic stage, the fetus can die within 1 week, therefore, we should strengthen the monitoring, self-counting of fetal movement and continuous electronic fetal heart rate monitoring, perform fetal biophysical scoring and combine with clinical, if necessary, terminate the pregnancy.