Doppler assessment of the pulsatility index in the cerebral circulation of the human fetus.

To determine whether the pulsatility index was similar in all cerebral vessels, 30 fetuses at 23 to 37 weeks' gestation were studied. There were 12 normal fetuses, 14 growth-retarded fetuses, and 4 fetuses that were transfused in utero because of Rh isoimmunization. The middle cerebral artery and the internal carotid artery were studied in all fetuses. The proximal anterior cerebral artery was also studied in addition to the other two vessels in 12 fetuses from the three groups. The pulsatility index was significantly higher in the middle cerebral artery than in the internal carotid artery in all three groups. The pulsatility index of the proximal anterior cerebral artery was between the values shown for the middle cerebral artery and the internal carotid artery. The pulsatility index of the proximal anterior cerebral artery was significantly different from the index for the middle cerebral artery and not significantly different from the index for the internal carotid artery. These data indicate the importance of knowing exactly which cerebral vessel is being insonated, so that the Doppler waveform can be interpreted correctly.