The normal value of umbilical artery s/d is not a fixed value, but varies with the gestational week of the pregnant woman, and usually the umbilical artery s/d ratio is less than 3 in a full-term pregnancy. Umbilical artery s/d ratio is the ratio of systolic pressure to diastolic pressure in the umbilical artery of the fetus, and is generally used to observe whether the development of the fetus is normal. In healthy fetuses, the s/d ratio is 3.5-5.5 before 24 weeks, 2.5-5 between 24 and 30 weeks, 2.5-4 between 30 and 36 weeks, and 1.7-3 between 36 and 40 weeks. s/d ratio decreases with the development of the fetus and the enlargement of the placenta under normal circumstances. In full-term pregnancy, if the ratio is greater than 3, fetal nutritional deficiencies and hypoxia are considered. If the fetus requires measurement of the s/d ratio of the umbilical artery, please consult a doctor and follow the doctor’s instructions if there is any abnormality.