The SD value is the ratio of systolic (S) to diastolic (D) of the umbilical artery during pregnancy, which is accurately called SD ratio clinically, and can reflect the blood flow of the umbilical cord. The SD ratio may be high due to mechanical obstruction of the umbilical cord blood flow; 2, decreased placental function: such as overdue pregnancy, placental aging, placental abruption, etc., resulting in insufficient placental blood perfusion, due to placental hypoxia and ischemia, resulting in fetal growth restriction, which may lead to a high SD ratio; 3, pregnancy complications: such as maternal gestational hypertension, anemia, etc., can lead to vasospasm, which in turn causes blood flow resistance The SD ratio can be increased by measuring the SD ratio. Under normal circumstances, the systolic (S) to diastolic (D) ratio of umbilical artery after full term is <3, and the SD ratio tends to decrease with the increase of gestational weeks. When the pregnant woman does not improve after treatment with oxygen, she should make proper treatment with the fetal heart monitoring results. If the fetal heart monitoring indicates class II or III monitoring, and the SD ratio continues to rise, the fetal biophysical score should be performed, and if the score is less than 6, intrauterine distress should be considered, and the pregnancy should be terminated by cesarean section.