title: A new non-invasive method for measuring uterine vascular resistance and its relationship to uterine artery Doppler indices: a longitudinal study.
abstract: OBJECTIVE
  To describe a new method for measuring uterine vascular resistance (R(uta) ), establish longitudinal reference ranges and explore the relationship between uterine artery (UtA) Doppler indices and R(uta) .
  
  
  METHODS
  This was a longitudinal study of 53 low-risk pregnancies. Doppler ultrasonography was used to measure UtA velocities, and the pulsatility index (PI), resistance index (RI) and systolic/diastolic velocity (S/D) ratio were calculated. R(uta) was calculated as a ratio between maternal mean arterial pressure and UtA time-averaged maximum velocity.
  
  
  RESULTS
  At 22 + 0 to 39 + 6 weeks of gestation, the mean R(uta) decreased from 1628 to 1180 dyne.s/cm(3) (P < 0.0001). UtA velocities increased (P < 0.0001), whereas the PI (0.79-0.56), RI (0.51-0.40) and S/D ratio (2.0-1.7) decreased (P < 0.0001). R(uta) and the UtA Doppler indices were positively associated (P = 0.003-0.001).
  
  
  CONCLUSIONS
  We describe a non-invasive method for measuring R(uta) and provide reference ranges for serial evaluation of UtA velocities, Doppler indices and R(uta) .
authors.affiliation: Faculty of Health Sciences, Women's Health and Perinatology Research Group, Department of Clinical Medicine, University of Tromsø, Tromsø, Norway.
authors.forename: K
authors.initials: K
authors.lastname: Flo
authors.forename: T
authors.initials: T
authors.lastname: Wilsgaard
authors.forename: G
authors.initials: G
authors.lastname: Acharya
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D011247:Pregnancy; D012039:Regional Blood Flow / Q000502:physiology; D015203:Reproducibility of Results; D018608:Ultrasonography, Doppler / Q000379:methods*; D016216:Ultrasonography, Prenatal / Q000379:methods; D055988:Uterine Artery / Q000000981:diagnostic imaging* / Q000502:physiology; D014599:Uterus / Q000098:blood supply / Q000000981:diagnostic imaging*; D014655:Vascular Resistance / Q000502:physiology*