Hourly fetal urinary production rate and blood velocity waveforms in the fetal renal artery relative to fetal heart rate pattern and fetal eye movements in normal pregnancies at 30-32 weeks of gestation.

In 14 normal pregnancies at 30-32 weeks of gestation, bloodflow velocity waveforms in the fetal renal artery and fetal micturition were studied in relation to fetal heart rate pattern (FHRP) and fetal eye movements. PI in the fetal renal artery was significantly lower in the presence of FHRP-B and eye movements separately and in combination compared with FHRP-A and absent eye movements separately and in combination. Fetal urinary output was higher in the absence of fetal eye movements. There was an inverse relationship between renal artery PI and fetal heart rate. However, since mean fetal heart rate in the various state variables was not essentially different, no standardization for heart rate was necessary. No correlation existed between renal artery PI and fetal urinary production rate. It can be concluded that in the normal fetus at 30-32 weeks of gestation, renal artery PI demonstrates a significant reduction in the presence of FHRP-B and fetal eye movements separately and in combination, suggesting reduced downstream impedance at renal level. However, the decrease in fetal micturition in the presence of fetal eye movements, suggests that reduced urinary output is determined by changes in fetal central nervous system activity rather than by changes in fetal renal perfusion.