Doppler ultrasonographic assessment of fetal renal artery blood flow velocity waveforms in intrauterine growth retarded fetuses.

Thirty-two blood flow velocity waveforms of the fetal renal artery, umbilical artery and fetal middle cerebral artery were recorded by a pulsed Doppler ultrasound from 28 to 38 gestational weeks in 32 intrauterine growth-retarded (IUGR) fetuses without structural defects. The nonstress test (NST) was performed on the day of pulsed Doppler ultrasonographic examination to assess fetal well-being. Of the 32 fetuses, the pulsatility index (PI: peak systolic velocity minus end diastolic velocity over mean velocity) values in the fetal renal artery were in the normal range in 26 measurements (81.3%), high in 2 (6.3%) and low in 4 (12.5%). The resistance index (RI: peak systolic velocity minus end diastolic velocity over peak systolic velocity) values in the umbilical artery and fetal middle cerebral artery were determined simultaneously in all the patients examined. Of the 12 fetuses with high RI values in the umbilical artery and low RI values in the fetal middle cerebral artery, the PI values in the fetal renal artery were within the normal range in 11 measurements (91.7%) and high in 1 (8.3%). Of the 9 fetuses with loss of fetal heart rate baseline variability in NST, the PI values in the fetal renal artery were within the normal range in 7 measurements (77.8%), high in 1 (11.1%) and low in 1 (11.1%). These data suggest that fetal renal blood flow may not change under the condition of chronic hypoxic state, although the NST shows fetal distress and the pulsed Doppler ultrasound reveals a brain sparing effect in the fetal middle cerebral artery. It is hypothesized that the fetal renal blood flow is controlled by an autoregulation mechanism for oxygen delivery presumably located in the renal artery.