Ebbing, Catherine, Rasmussen, Svein, Godfrey, Keith M., Hanson, Mark A. and Kiserud, Torvid
Fetal superior mesenteric artery: longitudinal reference ranges and evidence of regulatory link to portal liver circulation
Early Human Development, 85, (4), . (doi:10.1016/j.earlhumdev.2008.09.412).
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Objective: To establish longitudinal reference ranges for the fetal superior mesenteric artery (SMA) flow
velocity and pulsatility index (PISMA). Also to examine the hemodynamic relationship to venous liver
perfusion and umbilical flow distribution in the liver, to other splanchnic arteries, and more generally to the
middle cerebral and umbilical artery.
Methods: Prospective longitudinal study of 161 low-risk pregnancies using Doppler recordings including the
SMA, repeated on 3–5 occasions at 3–5 weekly intervals. Umbilical venous flow was estimated, blood velocity
in the shunt ductus venosus represented umbilico-caval (i.e. porto-caval) pressure gradient, and left portal
vein blood velocity represented umbilical distribution within the liver. The correlation between PISMA and the
splenic and hepatic artery PI were analysed (PISA and PIHA), and the association to middle cerebral and
umbilical artery PI (PIMCA and PIUA) assessed.
Results: Reference ranges for the SMA for gestational weeks 21–39 were based on 589 observations. Low
impedance in the SMA (i.e. low PISMA) was associated with low umbilical flow and porto-caval pressure
gradient (i.e. b10th centile), and high distribution of umbilical flow to the right lobe (i.e. left portal vein blood
velocity N90th centile). PISMA correlated weakly with PISA and PIHA (r=0.30, 95%CI 0.22–0.37, and r=0.39, 95%
CI 0.27–0.51, respectively). PISMA was positively associated with PIMCA and PIUA.
Conclusion: We have provided longitudinal reference ranges for fetal SMA flow velocity and PI, and shown
that the SMA, which perfuses the fetal gut, is also involved in the regulation of the liver perfusion.
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