title: Uterine artery pulsatility index in the three trimesters of pregnancy: effects of maternal characteristics and medical history.
abstract: OBJECTIVE
  To define the contribution of maternal variables that influence the measured uterine artery pulsatility index (UtA-PI) in screening for pregnancy complications.
  
  
  METHODS
  Maternal characteristics and medical history were recorded, and UtA-PI was measured, in women with a singleton pregnancy attending for three routine hospital visits at 11 + 0 to 13 + 6 weeks, 19 + 0 to 24 + 6 weeks and 30 + 0 to 34 + 6 weeks or 35 + 0 to 37 + 6 weeks' gestation. For pregnancies delivering phenotypically normal live births or stillbirths at ≥ 24 weeks' gestation, variables from maternal demographic characteristics and medical history that are important in the prediction of UtA-PI were determined from linear mixed-effects multiple regression.
  
  
  RESULTS
  UtA-PI was measured in 90 484 cases in the first trimester, 66 862 cases in the second trimester and 33 470 cases in the third trimester of pregnancy. Significant independent contributions to UtA-PI were provided by gestational age, maternal age, weight, racial origin and a history of pre-eclampsia (PE) in the previous pregnancy. Random-effects multiple regression analysis was used to define the contribution of maternal variables that influence the measured UtA-PI and express the values as multiples of the median (MoM). The model was shown to provide an adequate fit of MoM values for all covariates both in pregnancies that developed PE and in those that did not.
  
  
  CONCLUSIONS
  A model was fitted to express the measured UtA-PI as MoMs after adjustment for variables from maternal characteristics and medical history that affect this measurement.
authors.affiliation: Harris Birthright Research Centre for Fetal Medicine, King's College Hospital, London, UK.
authors.forename: A
authors.initials: A
authors.lastname: Tayyar
authors.affiliation: Harris Birthright Research Centre for Fetal Medicine, King's College Hospital, London, UK.
authors.forename: L
authors.initials: L
authors.lastname: Guerra
authors.affiliation: Institute of Health Research, University of Exeter, Exeter, UK.
authors.forename: A
authors.initials: A
authors.lastname: Wright
authors.affiliation: Institute of Health Research, University of Exeter, Exeter, UK.
authors.forename: D
authors.initials: D
authors.lastname: Wright
authors.affiliation: Harris Birthright Research Centre for Fetal Medicine, King's College Hospital, London, UK.
authors.forename: K H
authors.initials: KH
authors.lastname: Nicolaides
mesh_terms: D000328:Adult; D005260:Female; D005865:Gestational Age; D006305:Health Status Indicators; D006801:Humans; D000068097:Maternal Health / Q000706:statistics & numerical data*; D011237:Predictive Value of Tests; D011247:Pregnancy; D011248:Pregnancy Complications / Q000000981:diagnostic imaging / Q000209:etiology; D011264:Pregnancy Trimesters / Q000502:physiology*; D011446:Prospective Studies; D011673:Pulsatile Flow; D012044:Regression Analysis; D018617:Ultrasonography, Doppler, Pulsed; D016216:Ultrasonography, Prenatal / Q000379:methods / Q000706:statistics & numerical data; D055988:Uterine Artery / Q000000981:diagnostic imaging / Q000502:physiology*
keywords: first-trimester screening; pre-eclampsia; pyramid of pregnancy care; second-trimester screening; third-trimester screening; uterine artery Doppler