title: Modelling umbilical vein blood flow normograms at 14-40 weeks of gestation by quantile regression analysis.
abstract: OBJECTIVE
  To construct reference limits for gestation of umbilical vein blood flow (UVBF) in normal singleton pregnancies between 14 and 40 weeks of gestation using quantile regression.
  
  
  METHODS
  We ultrasonographycally examined 852 fetuses from low-risk pregnancies between 16 and 40 weeks of gestation in a prospective cross-sectional study. UV diameter and time-averaged maximum velocity (TAMXV) were measured in UV intra-abdominal portion by real time and Doppler ultrasonography. A semi-automatic measurement software was used to obtain UV diameter values. UVBF was then calculated from UV diameter and TAMXV measurements and expressed both as absolute value and as value normalized for fetal abdominal circumference (UVBF/AC). Individual centile values of the variables investigated were established by quantile regression in the gestational interval considered. In 50 cases UVBF was measured twice by the same investigator or by a second investigator and the intra- and inter-observer agreement were calculated.
  
  
  RESULTS
  A significant increase in UV diameter, TAMXV, UVBF absolute value and UVBF/AC was evidenced in the gestational period considered. Growth charts were established based on these measurements. The intra- and inter-observer intraclass correlation coefficients resulted as 0.92 (0.87-0.96) and 0.89 (0.84-0.97), respectively, for UBVF.
  
  
  CONCLUSIONS
  In this study we constructed UVBF charts using quantile regression in a large cohort of low-risk pregnancies. These charts offer the advantage of specific estimated regression parameters for each percentile, better defining the normal range of UVBF. This promises to be useful in the diagnosis and management of fetuses with abnormal fetal growth.
authors.affiliation: a Department of Obstetrics and Gynecology , Università di Roma "Tor Vergata" , Roma , Italy and.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Rizzo
authors.affiliation: b Operations Research Center, Massachusetts Institute of Technology , Cambridge , MA , USA.
authors.forename: Ludovica
authors.initials: L
authors.lastname: Rizzo
authors.affiliation: a Department of Obstetrics and Gynecology , Università di Roma "Tor Vergata" , Roma , Italy and.
authors.forename: Elisa
authors.initials: E
authors.lastname: Aiello
authors.affiliation: a Department of Obstetrics and Gynecology , Università di Roma "Tor Vergata" , Roma , Italy and.
authors.forename: Eugenio
authors.initials: E
authors.lastname: Allegra
authors.affiliation: a Department of Obstetrics and Gynecology , Università di Roma "Tor Vergata" , Roma , Italy and.
authors.forename: Domenico
authors.initials: D
authors.lastname: Arduini
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D003430:Cross-Sectional Studies; D005260:Female; D005317:Fetal Growth Retardation / Q000000981:diagnostic imaging / Q000503:physiopathology; D005865:Gestational Age; D006801:Humans; D008954:Models, Biological; D049451:Nomograms; D011247:Pregnancy; D012039:Regional Blood Flow; D012044:Regression Analysis; D016216:Ultrasonography, Prenatal; D014471:Umbilical Veins / Q000000981:diagnostic imaging / Q000502:physiology*; D055815:Young Adult
keywords: Doppler ultrasound; fetal growth; quantile regression; umbilical vein blood flow