title: Fetal superior mesenteric artery: longitudinal reference ranges and evidence of regulatory link to portal liver circulation.
abstract: OBJECTIVE
  To establish longitudinal reference ranges for the fetal superior mesenteric artery (SMA) flow velocity and pulsatility index (PI(SMA)). 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 PI(SMA) and the splenic and hepatic artery PI were analysed (PI(SA) and PI(HA)), and the association to middle cerebral and umbilical artery PI (PI(MCA) and PI(UA)) 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 PI(SMA)) was associated with low umbilical flow and porto-caval pressure gradient (i.e. <10th centile), and high distribution of umbilical flow to the right lobe (i.e. left portal vein blood velocity >90th centile). PI(SMA) correlated weakly with PI(SA) and PI(HA) (r=0.30, 95%CI 0.22-0.37, and r=0.39, 95%CI 0.27-0.51, respectively). PI(SMA) was positively associated with PI(MCA) and PI(UA).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Obsterics and Gynecology, Haukeland University Hospital, N-5021 Bergen, Norway. cathrine.ebbing@molmed.uib.no
authors.forename: Cathrine
authors.initials: C
authors.lastname: Ebbing
authors.forename: Svein
authors.initials: S
authors.lastname: Rasmussen
authors.forename: Keith M
authors.initials: KM
authors.lastname: Godfrey
authors.forename: Mark A
authors.initials: MA
authors.lastname: Hanson
authors.forename: Torvid
authors.initials: T
authors.lastname: Kiserud
mesh_terms: D005260:Female; D005333:Fetus / Q000098:blood supply*; D006801:Humans; D008099:Liver / Q000098:blood supply* / Q000196:embryology; D008137:Longitudinal Studies; D008638:Mesenteric Arteries / Q000000981:diagnostic imaging / Q000196:embryology*; D011247:Pregnancy; D011446:Prospective Studies; D016216:Ultrasonography, Prenatal