title: Fetal growth and birthweight standards as screening tools: methods for evaluating performance.
abstract: OBJECTIVE
  To discuss different methods for evaluating fetal growth and population-based birthweight standards relevant to different uses: either in antenatal care or in epidemiology.
  
  
  METHODS
  Population-based cohort study.
  
  
  METHODS
  Routinely collected data in Scotland.
  
  
  METHODS
  A total of 540,849 singletons born after 24 weeks between 1980 and 2003.
  
  
  METHODS
  The performance of a fetal growth standard and a population-based birthweight standard are compared in two ways. First, we consider the accuracy of estimated risks of stillbirth at any point during the remaining pregnancy, a measure that is relevant in antenatal care. Second, the rates of stillbirth at each gestation, which are measures relevant in epidemiology, are compared with the actual rates.
  
  
  METHODS
  Standard measures of screening and diagnostic performance: sensitivity, specificity, and positive and negative predictive values.
  
  
  RESULTS
  In clinical care, the evidence points towards using fetal growth standards: sensitivity at term is about 30%, increasing to 43% for preterm births (24-31 weeks of gestation), compared with about 29% across all ages under the birthweight standard. Positive predictive values are about 1% across gestations. For epidemiology, the evidence is not so clear-cut: preterm, the population birthweight standard has higher sensitivity and specificity, but this is not the case in the full-term weeks.
  
  
  CONCLUSIONS
  The performance of fetal growth and birthweight standards should be evaluated in different ways, depending on whether they are intended for use in antenatal care or in epidemiological investigations.
authors.affiliation: Department of Public Health, University of Birmingham, UK. k.hemming@bham.ac.uk
authors.forename: K
authors.initials: K
authors.lastname: Hemming
authors.forename: S
authors.initials: S
authors.lastname: Bonellie
authors.forename: J L
authors.initials: JL
authors.lastname: Hutton
mesh_terms: D001724:Birth Weight; D015331:Cohort Studies; D016021:Epidemiologic Studies; D005260:Female; D047109:Fetal Development; D057238:Growth Charts; D006801:Humans; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age; D011237:Predictive Value of Tests; D011247:Pregnancy; D011295:Prenatal Care; D011296:Prenatal Diagnosis / Q000379:methods*; D012016:Reference Values; D012606:Scotland; D012680:Sensitivity and Specificity; D050497:Stillbirth