title: Customised birthweight: coefficients for an Australian population and validation of the model.
abstract: BACKGROUND
  Published birthweight references in Australia do not fully take into account constitutional factors that influence birthweight and therefore may not provide an accurate reference to identify the infant with abnormal growth. Furthermore, studies in other regions that have derived adjusted (customised) birthweight references have applied untested assumptions in the statistical modelling.
  
  
  OBJECTIVE
  To validate the customised birthweight model and to produce a reference set of coefficients for estimating a customised birthweight that may be useful for maternity care in Australia and for future research.
  
  
  METHODS
  De-identified data were extracted from the clinical database for all births at the Mater Mother's Hospital, Brisbane, Australia, between January 1997 and June 2005. Births with missing data for the variables under study were excluded. In addition the following were excluded: multiple pregnancies, births less than 37 completed week's gestation, stillbirths, and major congenital abnormalities. Multivariate analysis was undertaken. A double cross-validation procedure was used to validate the model.
  
  
  RESULTS
  The study of 42,206 births demonstrated that, for statistical purposes, birthweight is normally distributed. Coefficients for the derivation of customised birthweight in an Australian population were developed and the statistical model is demonstrably robust.
  
  
  CONCLUSIONS
  This study provides empirical data as to the robustness of the model to determine customised birthweight. Further research is required to define where normal physiology ends and pathology begins, and which segments of the population should be included in the construction of a customised birthweight standard.
authors.affiliation: Centre for Clinical Studies, Mater Health Services, Brisbane, Queensland, Australia. scott.pain@mater.org.au
authors.forename: Scott
authors.initials: S
authors.lastname: Pain
authors.forename: Allan M Z
authors.initials: AM
authors.lastname: Chang
authors.forename: Vicki
authors.initials: V
authors.lastname: Flenady
authors.forename: Fung Y
authors.initials: FY
authors.lastname: Chan
mesh_terms: D001315:Australia; D001724:Birth Weight; D001827:Body Height; D015992:Body Mass Index; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D015233:Models, Statistical; D016011:Normal Distribution; D012016:Reference Values