Normal values of Pulsatility Index from fetal vessels: a cross-sectional study on 1556 healthy fetuses.

In a cross-sectional study of 1556 uncomplicated pregnancies velocity waveforms were recorded at the level of fetal umbilical artery, descending aorta, renal artery, internal carotid artery and middle cerebral artery. Reference limits for the Pulsatility Index of each vessel were constructed by regression analysis and a progressive fall during gestation was evidenced in all the vascular districts investigated with the exception of descending aorta. Furthermore we calculated the ratios between Pulsatility Index values of cerebral and peripheral vessels which may be relevant for the early diagnosis of the haemodynamic abnormalities occurring during the brain sparing effect.