ObjectiveTo test the hypothesis that after vibroacoustic stimulation the ratio between cerebral vascular and umbilical vascular resistance in the growth-restricted fetus is different from that in the normal fetus.MethodsThe pulsatility index (PI) of the middle cerebral artery and that of the umbilical artery (UA) were measured by pulsed Doppler velocimetry in 30 normal and 14 growthrestricted fetuses before and after vibronacoustic fetuses before and after vibroacoustic stimulation. The ratios of cerebral PI TO UA PI and the changes in PI after vibroacoustic stimulation were calculated. Comparisons were made using the Wilcoxon rank-sum test or signed-rank test. The statistical power of the study was 80%.ResultsMean (± standard deviation) cerebral PI values before vibroacoustic stimulation (1.50 ± 0.29 in normals and 1.29 ± 0.26 in the fetal growth restriction [FGR] group) and US PI values (1.00 ± 0.18 in normals and 1.15 ± 0.24 in the FGR group) were significantly different between groups (P< .04) and significantly decreased after vibroacoustic stimulation (P< .05). Although the cerebral to UA PI ratios (1.50 ± 0.38 in normals and 1.13 ± 0.33 in the FGR group) were significantly different between groups (P< .008), the values remained the same after vibroacoustic stimulation (P= .39 and 80, respectively). In all fetuses the fetal heart rate accelerated after vibroacoustic stimulation.ConclusionCerebral vascular resistance was lower and umbilical vascular resistance higher in the growth-restricted fetuses than in normals. The Vascular response after vibroacoustic stimulation in the growth-restricted fetus was not significantly different from the response of the normal fetus, suggesting preservation of regulation of resistance.