Use of umbilical-cerebral Doppler ratios in predicting fetal growth restriction in near-term fetuses.
OBJECTIVE: To compare the sensitivity and specificity of different umbilical-cerebral ratios in the prediction and detection of fetal growth restriction in near-term fetuses when the umbilical arterial waveform is within normal. METHODS: A prospective cross-sectional observational study was carried out recruiting consecutive singleton pregnancies with clinically suspected fetal growth restriction after 34 weeks gestation. The umbilical-cerebral ratios were then calculated from the S/D, RI and PI values and correlated with immediate perinatal outcome. RESULTS: A total of 187 patients were recruited. Twelve cases had abnormal UA Doppler flow velocity waveform studies. Of the 175 with normal UA Doppler findings, 92 (53.1%) were confirmed to have fetal growth restriction (FGR) with birth weights below the tenth centile for gestation. The detection rate of FGR by ultrasound biometry was 96.7%. The mean umbilical artery S/D, RI and PI values were higher in the fetal growth restriction group, while the middle cerebral artery values were lower as compared to fetuses with no growth restriction. A small but significant difference was seen in the umbilical-cerebral ratios of the different indices between the two groups. Receiver operator characteristic curves showed that there was little difference between the performances of the S/D, RI or PI ratios and all had limited power in predicting fetal growth restriction. CONCLUSION: In the presence of normal umbilical artery Doppler waveforms, umbilical-cerebral ratios have limited power to predict fetal growth restriction.