Fetal central blood flow alterations in human fetuses with umbilical artery reverse diastolic flow.

Blood flow velocimetry studies in animal fetuses with reverse diastolic flow in the umbilical artery have shown marked changes in the fetal central circulation characterized by a retrograde diastolic flow in the descending aorta, and as far as the aortic arch, along with a significant forward diastolic flow in the arteries going to the brain. Documentation and the implications of this phenomenon in human fetuses, to date, have not been reported. Doppler echographic evaluations of the diastolic patterns in the umbilical artery, descending aorta, the aortic arch, and the common carotid artery were performed on 5 fetuses in whom reverse diastolic flow was observed in the umbilical artery. In all five cases reverse diastolic flow was observed not only in the umbilical artery but also in the aortic arch. In the carotid artery, however, a forward diastolic flow was always recorded. It can be concluded, by inference, that in these fetuses, the area of lowest resistance was no longer the placenta, as seen in normal conditions, but the cerebral circulation. Furthermore, in four fetuses the retrograde component of the flow profiles was more prominent in the aortic arch compared with the descending aorta, suggesting that, in diastole, blood was coming from the pulmonary artery through the ductus arteriosus.