title: Doppler-derived umbilical artery absolute velocities and their relationship to fetoplacental volume blood flow: a longitudinal study.
abstract: OBJECTIVE
  To construct reference ranges for serial measurements of the umbilical artery (UA) absolute blood flow velocities in the second half of pregnancy and to test the hypothesis that significant associations exist between UA velocities and placental volume blood flow assessed from umbilical vein blood flow velocities and diameter.
  
  
  METHODS
  This was a prospective longitudinal study of the umbilical circulation. UA absolute velocities and umbilical vein blood flow were measured at 4-weekly intervals between 19 and 42 weeks' gestation in 130 low-risk singleton pregnancies. A total of 511 observations were used to construct the reference ranges and assess the association between UA absolute velocities and placental volume flow using multilevel modeling.
  
  
  RESULTS
  Both UA absolute velocities and placental volume blood flow showed a steady increase throughout the second half of pregnancy. However, the gestational age-related increase in the UA end-diastolic velocity (EDV) was greater than the corresponding increase in the peak systolic velocity (PSV). The time-averaged intensity-weighted mean velocity (TAWMV)/time-averaged maximum velocity (TAMXV) was 0.6 indicating probably not a completely parabolic velocity profile. There was a significant positive association (P < 0.00001) between UA absolute velocities and placental volume blood flow, but this association was modified by the gestational age. The intraobserver coefficients of variation for the UA PSV, EDV, TAMXV and TAWMV and placental volume blood flow were 10.17%, 16.29%, 11.46%, 18.18% and 8.61%, respectively.
  
  
  CONCLUSIONS
  We have established new reference ranges for the UA absolute velocities based on longitudinal data. They show a significant association with fetoplacental volume blood flow and may have a clinical value in the assessment of the umbilical circulation.
authors.affiliation: Department of Obstetrics and Gynecology, University Hospital of Northern Norway, Tromsø, Norway. ganesh.acharya@unn.no
authors.forename: G
authors.initials: G
authors.lastname: Acharya
authors.forename: T
authors.initials: T
authors.lastname: Wilsgaard
authors.forename: G K R
authors.initials: GK
authors.lastname: Berntsen
authors.forename: J M
authors.initials: JM
authors.lastname: Maltau
authors.forename: T
authors.initials: T
authors.lastname: Kiserud
mesh_terms: D000328:Adult; D000465:Algorithms; D001783:Blood Flow Velocity; D001810:Blood Volume; D005260:Female; D006801:Humans; D016014:Linear Models; D021041:Placental Circulation / Q000502:physiology*; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D011446:Prospective Studies; D012016:Reference Values; D012039:Regional Blood Flow; D018608:Ultrasonography, Doppler / Q000379:methods*; D016216:Ultrasonography, Prenatal / Q000379:methods*; D014469:Umbilical Arteries / Q000000981:diagnostic imaging* / Q000502:physiology