title: [Validity of classical fetal weight charts in the Portuguese population].
abstract: OBJECTIVE
  to assess the validity of several fetal weight charts, commonly used in Portugal, to classify its population.
  
  
  METHODS
  observational retrospective study. Singleton birth data was analyzed, from a two- year period (May 2008 to April 2010), from pregnancies with an ultrasound in the same institution, between the 8th and 14th gestational week. Upon data validation, percentiles for each completed gestational week were created, smoothed by a quadratic function, analyzed and compared to the tables more commonly utilized, in the institution and country, by using Z-scores, percentile comparison, sample 10th percentile detection sensibility and birthweight means comparison.
  
  
  RESULTS
  a total of 5,378 newborns (NB) were born in the period; 2,195 (42%) NB were included, born from the 24th to 42nd gestational week, allowing statistical analysis from the 34th to the 41st week. There were differences in the mean birthweight for each gestational age, between references and with the sample, as well as between sexes. The 10th percentile from some references has shown differences ranging from -288g at 37 weeks (-11% in Lubchenco et al. data), with and +133g at 34 weeks (+7,6% with Carrascosa et al. data) compared to the values found with the sample. Differences were also found concerning the sensitivity of the identification of a sample birthweight below the 10th percentile, which was between 14.1 and 100%, depending on the reference used.
  
  
  CONCLUSIONS
  the limitation of these kinds of reference values must be remembered and minimized, with the adoption of regionally or nationally produced references, contemplating other variables, such as sex, with precisely known gestation duration and with validation of the utilized references in loco.
authors.affiliation: Médico Interno do Serviço de Obstetrícia e Ginecologia do Centro Hospitalar do Alto Ave – Guimarães, Portugal. ricardo.fs.santos@gmail.com
authors.forename: Ricardo Filipe Sousa
authors.initials: RF
authors.lastname: Santos
authors.forename: Rui Filipe Oliveira
authors.initials: RF
authors.lastname: Miguelote
authors.forename: Diana Maria da Silva
authors.initials: DM
authors.lastname: Coelho
authors.forename: Ana Maria Alves Vieira
authors.initials: AM
authors.lastname: Andrade
authors.forename: Cristina Maria Nogueira da Costa
authors.initials: CM
authors.lastname: Santos
authors.forename: João Francisco Montenegro de Andrade Lima
authors.initials: JF
authors.lastname: Bernardes
authors.forename: Ricardo João
authors.initials: RJ
authors.lastname: Cruz-Correia
mesh_terms: D005260:Female; D020567:Fetal Weight; D005865:Gestational Age; D057238:Growth Charts; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D011174:Portugal; D012016:Reference Values; D015203:Reproducibility of Results; D012189:Retrospective Studies