Doppler velocimetry of the aortic isthmus in human fetuses with abnormal velocity waveforms in the umbilical artery.

Experimental studies in animals using Doppler ultrasound suggest that hemodynamic disturbances during fetoplacental circulatory insufficiency will be detected at an earlier and less severe stage in the aortic isthmus compared to the umbilical artery. In cases in which more severe impairment of the placental circulation was achieved, reverse flow was recorded in the aortic isthmus before its appearance in the umbilical artery. The present study was undertaken to investigate whether the same findings could be demonstrated in the aortic isthmus of the human fetus. The video recordings of 100 fetuses with abnormal umbilical artery pulsatility index were reviewed. Qualitative abnormalities of the Doppler waveform, i.e., absence or reversal of end-diastolic velocities, were more frequently found in the aortic isthmus (absent 28%, reversed 41%) compared to the fetal end of the umbilical artery (absent 20%, reversed 19%; p < 0.0001) and also more frequently found in the fetal end compared to the placental end (absent 13%, reversed 2%; p < 0.0001). This study confirms our previous observations of the aortic isthmus as a site for early detection of fetoplacental hemodynamic disturbances. Reverse diastolic flow in the isthmus could direct poorly oxygenated blood from the descending aorta towards the carotid arteries and the brain. Further prospective studies are needed to establish the clinical value of these findings in terms of perinatal morbidity and, more importantly, of long-term neurological impairment.