title: Longitudinal reference ranges for ductus venosus flow velocities and waveform indices.
abstract: OBJECTIVE
  Serial Doppler measurements of the ductus venosus are used increasingly for monitoring fetuses at risk of hemodynamic compromise, but existing reference ranges are based on cross-sectional studies and thus are less suitable for comparison with serial measurements. We aimed to establish longitudinal reference ranges for ductus venosus flow velocities and waveform indices and to provide the necessary terms for calculating conditional reference ranges for serial measurements.
  
  
  METHODS
  This was a longitudinal study of 160 low-risk pregnancies. Pulsed Doppler ultrasound was used to record ductus venosus blood flow velocities at 4-week intervals from 20-22 weeks of gestation onwards.
  
  
  RESULTS
  With a success rate of 93%, 547 measurements (four or five in each fetus) were used to establish reference ranges. The time-averaged maximum velocity was 50 cm/s at 21 weeks of gestation, increased to 60 cm/s at 32 weeks, and remained so until term. Similarly, the peak systolic velocity increased from 59 cm/s at 21 weeks to 71 cm/s at 31 weeks and remained so until term. The end-diastolic velocity showed a continuous increase from 31 cm/s at 21 weeks to 43 cm/s at 40 weeks. The pulsatility index for veins decreased from 0.57 at 21 weeks to 0.44 at 40 weeks. When conditioned by a previous measurement, the reference ranges for the next observation became narrower and commonly shifted compared with those of the entire population.
  
  
  CONCLUSIONS
  The new longitudinal reference ranges presented here reflect the development of the ductus venosus flow velocities and velocity indices and are thus appropriate for serial measurements, particularly if conditional terms are included.
authors.affiliation: Department of Clinical Medicine, Section of Obstetrics and Gynaecology, University of Bergen, Bergen, Norway. jorg.kessler@kk.uib.no
authors.forename: J
authors.initials: J
authors.lastname: Kessler
authors.forename: S
authors.initials: S
authors.lastname: Rasmussen
authors.forename: M
authors.initials: M
authors.lastname: Hanson
authors.forename: T
authors.initials: T
authors.lastname: Kiserud
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology*; D003430:Cross-Sectional Studies; D005260:Female; D005318:Fetal Heart / Q000000981:diagnostic imaging / Q000502:physiology*; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D008099:Liver / Q000098:blood supply; D008137:Longitudinal Studies; D011247:Pregnancy; D012016:Reference Values; D018608:Ultrasonography, Doppler / Q000379:methods; D014471:Umbilical Veins / Q000000981:diagnostic imaging* / Q000196:embryology; D014682:Vena Cava, Inferior / Q000000981:diagnostic imaging* / Q000196:embryology