Renal artery flow-velocity waveforms in normal and hypoxemic fetuses.

Color flow mapping was used to identify the fetal renal artery and to obtain flow-velocity waveforms. A reference range of the fetal renal artery pulsatility index with gestation was constructed from a cross-sectional study of 114 appropriate for gestational age fetuses of 17 to 43 weeks' gestation. The pulsatility index decreased linearly with gestation, indicating a fall in impedance to flow, and presumably an increase in renal perfusion. The renal artery pulsatility index was also determined in 18 small-for-gestational-age fetuses and was higher than the appropriate-for-gestational-age group. The small-for-gestational-age fetuses also had fetal blood sampling performed by cordocentesis. A significant, direct correlation was found between blood oxygen deficit and increased renal artery pulsatility index.