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Blood flow in the umbilical artery during labor
Last reviewed: 04.07.2025
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Modern studies show that cardiotocography does not have significant advantages over conventional fetal auscultation with an obstetric stethoscope. Thus, in 1988, the American Association of Obstetricians and Gynecologists concluded that periodic fetal auscultation during labor "is as effective as electronic fetal monitoring in monitoring high-risk patients during labor." Despite this, many obstetric centers conduct monitoring during labor. There is a poor relationship between pathological KIT and fetal acidosis, but the chances of fetal acidosis are higher with pathological CTG.
Low variability also correlates poorly with fetal acidosis and can be predicted in no more than 5% of fetuses. When tachycardia or decelerations are observed during labor, the predicted pH of 7.20 increases to 30%. Late decelerations predict fetal acidosis between 30-40%. Late decelerations and the prediction of an Apgar score of 7 or less are more related to the size of the deceleration than to the temporal relationship with uterine contractions.
Furthermore, the use of intrapartum CTG has not reduced perinatal mortality, but has only reduced neonatal injury. Therefore, CTG and fetal acid-base balance are necessary in high-risk women for optimal management of labor. For example, in England, less than half of obstetric centers use CTG and fetal acid-base balance. Only low umbilical artery pH values are correlated with low Apgar scores, but neither pH nor Apgar predict neonatal neurological morbidity. Therefore, intermittent intrapartum hypoxia does not significantly correlate with subsequent neurological outcome in the newborn. Continuous monitoring improves the condition of 1 in 1,000 babies monitored during labor, but the incidence of cesarean sections and obstetric forceps has increased significantly as a result of this practice.
Measuring the blood flow in the umbilical artery is even more preferable than CTG in detecting fetal distress during labor, since fetal distress increases the rate of cesarean sections by 12 times. The pulsation index does not change significantly during labor. During contractions, it changes only if the fetus has heartbeat decelerations. An altered index was most often observed in fetal hypotrophy, and therefore accurate determination of the blood flow in the umbilical artery is essential in predicting fetal hypotrophy, and the absence of end-diastolic blood flow in 80% gives hypoxia and in 46% the risk of developing acidosis.
In late labor, an increase in the pulsatility index by 20% in the internal carotid artery during maternal hyperoxygenation (60% O2 inhalation ) is a marker of an unfavorable outcome of late labor for the fetus.
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