title: Reference range for uterine artery Doppler pulsatility index using transvaginal ultrasound at 20-24w6d of gestation in a low-risk Brazilian population.
abstract: OBJECTIVE
  To establish reference range for uterine artery (UtA) Doppler pulsatility index (PI) using transvaginal ultrasound at 20-24w6d of gestation in a Brazilian population.
  
  
  METHODS
  A retrospective cross-sectional study in 847 low-risk pregnant women undergoing routine second trimester ultrasound examination was conducted from February 2012 through March 2015. The mean UtA PI was calculated using color Doppler ultrasound with UtA gated at the level of the internal os. Mean±standard deviation and ranges for UtA Doppler PI in relation to gestational age (GA) are reported. Polynomial regression was used to obtain the best fit using mean UtA Doppler PI and GA (weeks) with adjustments performed using determination coefficient (R(2)). The 5(th), 50(th), and 95(th) percentiles for the mean UtA Doppler PI in relation to GA were determined.
  
  
  RESULTS
  The mean UtA Doppler PI ranged from 1.14 at 20 weeks to 0.95 at 24 weeks of gestation. The best-fit curve of mean UtA Doppler PI as a function of GA was a first-degree polynomial regression: mean UtA Doppler PI=1.900-0.038×GA (R(2)=0.01).
  
  
  CONCLUSIONS
  In summary, when the mean UtA PI Doppler values were measured by transvaginal ultrasound at 20-24w6d of gestation, decrease in UtA Doppler PI values with advancing GA was observed. Reference range for the mean UtA Doppler PI at 20-24w6d of gestation using the transvaginal ultrasound in a low-risk Brazilian population was established. We believe that this reference range may be of clinical value in daily obstetric practice.
authors.affiliation: Mario Palmério University Hospital - University of Uberaba (UNIUBE), Uberaba-MG, Brazil; Radiologic Clinic of Uberaba (CRU), Uberaba-MG, Brazil.
authors.forename: Alberto Borges
authors.initials: AB
authors.lastname: Peixoto
authors.affiliation: Mario Palmério University Hospital - University of Uberaba (UNIUBE), Uberaba-MG, Brazil; Radiologic Clinic of Uberaba (CRU), Uberaba-MG, Brazil.
authors.forename: Taciana Mara Rodrigues
authors.initials: TM
authors.lastname: Da Cunha Caldas
authors.affiliation: Department of Obstetrics and Gynecology, Prenatal Diagnostic Center, Guastalla Civil Hospital, Reggio Emilia, Italy.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Tonni
authors.affiliation: Radiologic Clinic of Uberaba (CRU), Uberaba-MG, Brazil.
authors.forename: Priscilla
authors.initials: P
authors.lastname: De Almeida Morelli
authors.affiliation: Radiologic Clinic of Uberaba (CRU), Uberaba-MG, Brazil.
authors.forename: Larissa D'amico
authors.initials: LD
authors.lastname: Santos
authors.affiliation: Department of Obstetrics and Gynecology, Ribeirão Preto Medical School, University of São Paulo (DGO-FMRP-USP), Ribeirão Preto-SP, Brazil.
authors.forename: Wellington P
authors.initials: WP
authors.lastname: Martins
authors.affiliation: Department of Obstetrics, Paulista School of Medicine - Federal University of São Paulo (EPM-UNIFESP), São Paulo-SP, Brazil.
authors.forename: E
authors.initials: E
authors.lastname: Araujo Júnior
keywords: Uterine Doppler artery; reference range; second trimester