Discordant blood flow velocity waveforms in left and right brachial arteries in growth-retarded fetuses

To determine if the increase in cerebral blood flow (“brain-sparing” effect) with fetal hypoxemia is associated with discordant hemodynamics in the upper extremities. We studied 12 fetuses with severe growth retardation, absent or reverse end-diastolic blood flow in the umbilical artery, and low pulsatility index (PI) in the middle cerebral artery, and 12 appropriately grown control fetuses with normal fetoplacental Doppler studies. The right and left brachial arteries were identified by high-resolution color Doppler ultrasonography, and the PI was measured in each brachial artery. All growth-retarded fetuses had lower impedance indices in the right than in the left brachial artery (mean API 1.0, 95% confidence interval [CI] 0.7–1.3, P < .001). No differences in the brachial artery impedance indices were found in control fetuses matched for gestational age (mean ΔPI 0.0, 95% CI −0.2 to 0.2). Left and right brachial artery blood flow velocity waveforms are discordant in fetuses with growth retardation and cerebral vasodilation. Because the right arm receives its blood supply from the same source as the brain (brachiocephalic artery) and given the proximity of the left subclavian artery to the ductus arteriosus, we speculate that this might be the result of increased blood flow into the brachiocephalic circulation and/or functional differences in the distribution of left and right ventricular output within the aortic arch in response to fetal hypoxemia.