The cerebroumbilical ratio (also called the cerebroplacental ratio) can be used to evaluate a fetus.
Analysis: Doppler ultrasound (based on a trace of at least consecutive waveforms, in the absence of fetal breathing movements and in the absence of uterine contractions, with the angle of insonation less than 30 degrees.
Paramters:
(1) pulsatility index of the middle cerebral artery (MCA)
(2) pulsatility index of the umbilical artery (UA)
cerebroumbilical ratio =
= (pulsatility index of MCA) / (pulsatility index of UA)
Interpretation:
• The mean UA PI for the cohort reported by Prior et al was 0.80 while the MCA PI was 1.37. The mean ratio for the cohort was 1.77.
• Normally the ratio peaks at the 34 week of gestation then slowly declines.
• A fetus with a ratio less than the 10th percentile for gestational age is at increased risk for fetal compromise.
• A ratio > 90th percentile excludes fetal compromise with Cesarean section.
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