Fetal blood flow velocity waveforms in pregnancies complicated by intrauterine growth retardation.

Fifty-three pregnancies suspected for a small-for-gestational age fetus (SGA) by ultrasonographic weight estimation (below the 10th percentile of Brenner nomograms) were studied using pulsed Doppler (Duplex) for recording fetal blood flow velocity waveforms from the umbilical artery and fetal internal carotid artery. The pulsatility index (PI) for each artery was calculated as an index of vascular resistance. The gestational age ranged from 29 to 40 weeks. In 42 cases an SGA newborn was delivered (according to Brenner tables corrected for maternal parity and fetal sex), 34 newborns were SGA according to Usher and McLean (2 SD below the mean). Fetal structural and/or chromosomal defects were found in four cases, all of which showed symmetric intrauterine growth retardation and normal PI values in the fetal internal carotid artery. After excluding the infants with congenital abnormalities and using nomograms constructed for our own population, the ratio between the PI of the umbilical artery and the internal carotid artery was found to be the best predictor of SGA (sensitivity 84.2%, specificity 90.9%, positive predictive value 97.0%, negative predictive value 62.5%). Using the more demanding criteria for SGA according to Usher and McLean, sensitivity improved to 100%, specificity was 80.0%, positive predictive value 87.9%, and negative predictive value 100%.