title: Contingent screening for preterm pre-eclampsia.
abstract: OBJECTIVE
  Effective screening for pre-eclampsia resulting in delivery < 37 weeks' gestation (preterm PE) is provided by assessment of a combination of maternal factors, mean arterial pressure (MAP), uterine artery pulsatility index (UtA-PI) and serum placental growth factor (PlGF) at 11-13 or 19-24 weeks' gestation. This study explores the possibility of carrying out routine screening for preterm PE by maternal factors and MAP in all pregnancies and reserving measurements of UtA-PI and PlGF for a subgroup of the population, selected on the basis of the risk derived from screening by maternal factors and MAP alone.
  
  
  METHODS
  Study data were derived from prospective screening for adverse obstetric outcomes in women attending their routine hospital visit at 11-13 and/or 19-24 weeks' gestation. Bayes' theorem was used to derive the a-priori risk for preterm PE from maternal factors and MAP. The posterior risk was obtained by the addition of UtA-PI and PlGF. We estimated the detection rate (DR) of preterm PE, at an overall false-positive rate (FPR) of 10%, from a policy in which first-stage screening by a combination of maternal factors and MAP defines screen-positive, screen-negative and intermediate-risk groups, with the latter undergoing second-stage screening by UtA-PI and PlGF.
  
  
  RESULTS
  At 11-13 weeks' gestation, the model-based DR of preterm PE, at a 10% FPR, when screening the whole population by maternal factors, MAP, UtA-PI and PlGF was 74%. A similar DR was achieved by two-stage screening, with screening by maternal factors and MAP in the first stage and reserving measurement of UtA-PI and PlGF for the second stage and for only 50% of the population. If second-stage screening was offered to 30% of the population, there would be only a small reduction in DR from 74% to 71%. At 19-24 weeks, the model-based DR of preterm PE, at a 10% FPR, when screening the whole population by maternal factors, MAP, UtA-PI and PlGF was 84%. A similar DR was achieved by two-stage screening with measurements of UtA-PI and PlGF in only 70% of the population; if second-stage screening was offered to 40% of the population, the DR would be reduced from 84% to 81%.
  
  
  CONCLUSIONS
  High DR of preterm PE can be achieved by two-stage screening in the first and second trimesters with maternal factors and MAP in the whole population and measurements of UtA-PI and PlGF in only some of the pregnancies. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
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: D M
authors.initials: DM
authors.lastname: Gallo
authors.affiliation: Harris Birthright Research Centre for Fetal Medicine, King's College Hospital, London, UK.
authors.forename: S
authors.initials: S
authors.lastname: Gil Pugliese
authors.affiliation: Harris Birthright Research Centre for Fetal Medicine, King's College Hospital, London, UK.
authors.forename: C
authors.initials: C
authors.lastname: Casanova
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: D062186:Arterial Pressure; D001499:Bayes Theorem; D005260:Female; D005865:Gestational Age; D006801:Humans; D000072483:Placenta Growth Factor / Q000097:blood*; D011225:Pre-Eclampsia / Q000175:diagnosis*; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods; D011446:Prospective Studies; D055988:Uterine Artery / Q000502:physiology*
chemical_list: C000608036:PGF protein, human; D000072483:Placenta Growth Factor
keywords: Bayes' theorem; contingent screening; mean arterial pressure; placental growth factor; pre-eclampsia; pyramid of pregnancy care; survival model; uterine artery Doppler