Blood flow velocity waveforms in the middle cerebral, renal and femoral arteries of human fetuses

Abstract Objective: To establish normal reference values for blood flow velocity indices in the human fetal middle cerebral, renal and femoral arteries. Methods: In a cross-sectional study, 83 fetuses in uncomplicated pregnancies were examined. The umbilical artery was also studied to obtain the ratio between blood flow indices in the middle cerebral artery and umbilical artery. Results: Pulsatility index (PI) in the middle cerebral artery manifested an increase in the late second trimester and early third trimester, followed by a fall toward term. Time averaged maximum velocity in the middle cerebral artery increased with advancing gestational age, starting at about 27 weeks of gestation. PI in the renal artery did not manifest any change with advancing gestational age. The femoral artery manifested an increasingly pulsatile pattern with advancing gestational age, and reverse flow in early diastole was first noted at 30 gestational weeks. PI values increased in the third trimester of pregnancy. The umbilical artery PI decreased linearly with advancing gestation. The ratio between the middle cerebral artery PI and the umbilical artery PI increased until 29 weeks' gestational age, then decreased slightly until term. Conclusions: The study demonstrated that in the healthy fetus, the physiological development of PI with gestational age varies from one vessel bed to another. For clinical purposes, gestational age-related and apparatus-specific reference curves of waveform indices should be used.