title: Reference ranges for serial measurements of umbilical artery Doppler indices in the second half of pregnancy.
abstract: OBJECTIVE
  The purpose of this study was to construct new reference ranges for serial measurements of commonly used umbilical artery Doppler indices (pulsatility index, resistance index, and systolic:diastolic ratio).
  
  
  METHODS
  This was a prospective longitudinal study of the umbilical artery Doppler indices that were obtained serially at the free-loop of umbilical cord at 4-week intervals at 19 to 42 weeks of gestation in 130 low-risk singleton pregnancies. A total of 513 observations were used to construct the reference ranges with the use of multilevel modeling.
  
  
  RESULTS
  Longitudinally established percentiles of Doppler indices from the present study show a continuous reduction throughout the second half of pregnancy without any plateau or increase near term, as reported previously. There was a significant negative association between Doppler indices and placental weight and neonatal birth weight, but not with gender. The intraobserver coefficients of variation for the umbilical artery pulsatility index, resistance index, and systolic:diastolic ratio were 10.5%, 6.8 %, and 13.0 %, respectively.
  
  
  CONCLUSIONS
  New reference ranges for umbilical artery Doppler indices that are based on longitudinal observations appear to be slightly different from cross-sectional studies and are more appropriate for serial evaluation of fetal hemodynamics.
authors.affiliation: Department of Obstetrics and Gynecology, University Hospital of Northern Norway, Tromsø, Norway. ganesh.acharya@unn.no
authors.forename: Ganesh
authors.initials: G
authors.lastname: Acharya
authors.forename: Tom
authors.initials: T
authors.lastname: Wilsgaard
authors.forename: Gro K Rosvold
authors.initials: GK
authors.lastname: Berntsen
authors.forename: Jan Martin
authors.initials: JM
authors.lastname: Maltau
authors.forename: Torvid
authors.initials: T
authors.lastname: Kiserud
mesh_terms: D000293:Adolescent; D000328:Adult; D001724:Birth Weight; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008137:Longitudinal Studies; D008297:Male; D015588:Observer Variation; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D011446:Prospective Studies; D012016:Reference Values; D012737:Sex Factors; D018608:Ultrasonography, Doppler; D014469:Umbilical Arteries / Q000033:anatomy & histology / Q000000981:diagnostic imaging*