What does a high fetal umbilical artery SD value indicate?

The umbilical artery SD value is one of the important indicators to measure the health of the fetus. During prenatal examinations, the umbilical artery SD value is generally tested. At different gestational weeks, a high umbilical artery SD value indicates different problems. For example, at 26 to 28 weeks of pregnancy, a high umbilical artery SD value indicates that the fetus has malformations, umbilical cord abnormalities, placental dysfunction, developmental delay, etc. After 36 to 37 weeks, if the umbilical artery SD value is still high, it indicates a poor perinatal prognosis.

Stage 1: If the S/D and RI values ​​increase during the 26th to 28th week of pregnancy (after 28 weeks, S/D should be less than 3 and RI should be less than 0.8)

The main considerations are :

(1) Fetal malformation: Fetal congenital diseases are closely related to umbilical artery resistance and should be further examined by B-ultrasound.

(2) Umbilical cord abnormality: When the umbilical cord is entangled, too long or too short, or too thin, affecting the placental circulation, the blood flow impedance index will become abnormal. If the S/D value is higher than normal and ultrasound shows abnormal conditions such as the umbilical cord around the neck, the baby should be closely observed according to the stage of pregnancy.

(3) Placental dysfunction: Pathological changes in the placenta can lead to a decrease in placental volume, a decrease in the total cross-sectional area of ​​effective blood vessels, and an increase in blood flow resistance, resulting in a decrease in blood perfusion.

(4) Intrauterine growth retardation (IUGR): There are many reasons for pregnant women to suffer from IUGR. In addition to genetic nutrition, harmful contact, malformation, viruses and other factors, the proportion of IUGR caused by pregnancy appendages such as the placenta is increasing, which is manifested by increased S/D and RI values.

The second stage: monitoring after 36-37 weeks, umbilical artery blood flow impedance is divided into three levels

Level 1: S/D value <3.0, umbilical artery blood flow impedance is at a normal level.

Grade 2: S/D value > 3.0 but < 4.0, which will not cause acute fetal distress and should be treated promptly to prevent the condition from worsening.

Level 3: S/D value>4.0, which will lead to poor perinatal prognosis.

Phase III: Umbilical artery impedance index during labor

When a normal pregnant woman is about to give birth, there is no obvious change in the S/D value. If the indicator is abnormal, it indicates a poor perinatal prognosis.

If abnormal umbilical cord blood flow is diagnosed, it is best to count fetal movements every day to monitor the fetal condition. If the abnormal umbilical cord blood flow is not very serious, it is recommended to lie on the left side. If there is no improvement, oxygen therapy is required if necessary.

The ratio of the maximum blood flow velocity during systole (S) to the blood flow velocity during end diastole (D) of the umbilical artery (S/D, A/B). By observing the dynamic changes of the S/D (A/B) ratio, the development of the placenta can be judged. Under normal circumstances, as the fetus develops, the placenta gradually increases in size, vascular resistance gradually decreases, and the S/D (A/B) ratio gradually decreases. From 25 to 41 weeks of pregnancy, the S/D ratio decreased almost linearly from 2.8 to 2.2. The fetus has intrauterine growth retardation, the placenta and fetus are poorly developed, the placenta does not increase in size, and vascular resistance does not decrease. Therefore, the S/D ratio does not decrease. Clinically, if S/D does not decrease regularly or even increases, it indicates that the fetus is maldeveloped.