Umbilical Cord Blood Flow Normal Value Reference Table
May 22, 2022
Source: Cainiu Health
Dr. Chen Zhe
Introduction
Normal values for umbilical blood flow vary according to gestational age, with three primary parameters assessed. Typically, an S/D ratio ≤3.0 in the third trimester is considered normal. Umbilical blood flow assessment aims to evaluate fetal development within the uterus; abnormalities—including fetal disorders and congenital malformations—may sometimes be reflected by abnormal umbilical blood flow patterns. Abnormal umbilical blood flow may also be associated with placental developmental defects and histological abnormalities.
Every parent hopes their baby will grow up healthy and strong—but prenatal examinations are even more critical. Assessing fetal well-being through prenatal screening and monitoring—including umbilical cord blood flow indices—is essential for evaluating fetal health. So, what are the normal reference values for umbilical cord blood flow?
Normal Reference Values for Umbilical Cord Blood Flow
Umbilical cord blood flow parameters vary with gestational age and primarily include three key indices, with the S/D (systolic-to-diastolic) ratio serving as the principal indicator. In late pregnancy, an S/D ratio ≤3.0 is generally considered normal. The purpose of umbilical cord blood flow assessment is to evaluate fetal development within the uterus—specifically, to detect potential complications such as intrauterine growth restriction (IUGR), predisposition to pregnancy-induced hypertension (PIH), or intrauterine hypoxia. Abnormal umbilical blood flow may also be associated with fetal anomalies, congenital malformations, or placental developmental defects.
Umbilical cord blood flow correlates closely with gestational age, typically decreasing progressively as pregnancy advances. At 24 weeks’ gestation, the average normal umbilical artery S/D ratio is 3.4, with an upper limit of 4.25; values exceeding this threshold are considered abnormal. Umbilical artery blood flow can be assessed using a dedicated umbilical artery Doppler flow analyzer, which measures blood flow from the fetal limb side. Built-in software automatically calculates and classifies vascular resistance based on measured parameters—including the S/D ratio, pulsatility index (PI), resistance index (RI), and fetal umbilical resistance (FUR).
Umbilical cord blood flow assessment is highly important. In routine prenatal care, it is advisable to perform this test once the fetus has reached an appropriate developmental stage. If abnormalities are detected, prompt and effective interventions should be initiated. We hope this information is helpful to you! Wishing you good health and happiness!
