title: Low umbilical artery vascular flow resistance and fetal outcome.
abstract: BACKGROUND
  An abnormally high [above mean + 2 standard deviations (SD)] umbilical artery (UA) pulsatility index (PI) indicates impaired fetal outcome, whereas the impact of an "abnormally" low (below mean -2 SD) PI is unknown.
  
  
  METHODS
  Perinatal outcome was compared between cases with a UA PI less than mean -2 SD (group A: high-risk cases selected from a database, n = 330; group B: unselected cases, n = 39) and unselected controls (group C) with a PI within mean +/- 2 SD (n = 863) at Doppler velocimetry. Groups B and C were retrieved from a population-based sample. The unpaired t-test, Mann-Whitney U-test, chi(2)-test and Fisher's exact probability test were used for statistical comparisons with a two-tailed p < 0.05 being significant.
  
  
  RESULTS
  No significant differences were found between group A vs. group C and group B vs. group C regarding perinatal mortality, Apgar scores at 1, 5 or 10 min, or arterial or venous cord blood pH. Postterm pregnancy in group A carried no additional risk. For obvious reasons, operative delivery and neonatal intensive care were more common in group A than in group C, but no such differences were found between groups B and C. The mean birthweight was 3.7% higher in group B than in group C (p = 0.049).
  
  
  CONCLUSIONS
  Deeming a UA PI below the lower reference limit as "abnormally" low is a statistical definition that was not reflected by a biological imperfection. Instead, a low UA PI promoted fetal growth.
authors.affiliation: Department of Obstetrics and Gynecology, Malmö University Hospital, S-205 02 Malmö, Sweden. per.olofsson@obst.mas.lu.se
authors.forename: Per
authors.initials: P
authors.lastname: Olofsson
authors.forename: Hanna
authors.initials: H
authors.lastname: Olofsson
authors.forename: Johan
authors.initials: J
authors.lastname: Molin
authors.forename: Karel
authors.initials: K
authors.lastname: Marsál
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D016022:Case-Control Studies; D005260:Female; D005333:Fetus / Q000098:blood supply*; D006801:Humans; D011247:Pregnancy; D011256:Pregnancy Outcome; D011673:Pulsatile Flow; D013548:Sweden / Q000453:epidemiology; D014469:Umbilical Arteries / Q000502:physiology*; D014655:Vascular Resistance