title: When is birthweight at term abnormally low? A systematic review and meta-analysis of the association and predictive ability of current birthweight standards for neonatal outcomes.
abstract: BACKGROUND
  Intrauterine growth restriction is a cause of neonatal morbidity and mortality. A variety of definitions of low birthweight are used in clinical practice, with a lack of consensus regarding which definitions best predict adverse outcomes.
  
  
  OBJECTIVE
  To evaluate the relationship between birthweight standards and neonatal outcome in term-born infants (at ≥ 37 weeks of gestation).
  
  
  METHODS
  MEDLINE (1966-January 2011), EMBASE (1980-January 2011), and the Cochrane Library (2011:1) and MEDION were included in our search.
  
  
  METHODS
  Studies comprising live term-born infants (gestation ≥ 37 completed weeks), with weight or other anthropometric measurements recorded at birth along with neonatal outcomes.
  
  
  METHODS
  Data were extracted to populate 2 × 2 tables relating birthweight standard with outcome, and meta-analysis was performed where possible.
  
  
  RESULTS
  Twenty-nine studies including 21 034 114 neonates were selected. Absolute birthweight was strongly associated with mortality, with birthweight < 1.5 kg giving the largest association (OR 48.6, 95% CI 28.62-82.53). When using centile charts, regardless of threshold, the summary odds ratios were significant but closer to 1 than when using absolute birthweight. For all tests, summary predictive ability comprised high specificity and positive likelihood ratio for neonatal death, but low sensitivity and a negative likelihood ratio close to 1.
  
  
  CONCLUSIONS
  Absolute birthweight is a prognostic factor for neonatal mortality. The indirect evidence suggests that centile charts or other definitions of low birthweight are not as strongly associated with mortality as the absolute birthweight. Further research is required to improve predictive accuracy.
authors.affiliation: School of Medicine, the University of Nottingham, Nottingham, UK.
authors.forename: G L
authors.initials: GL
authors.lastname: Malin
authors.forename: R K
authors.initials: RK
authors.lastname: Morris
authors.forename: R
authors.initials: R
authors.lastname: Riley
authors.forename: M J
authors.initials: MJ
authors.lastname: Teune
authors.forename: K S
authors.initials: KS
authors.lastname: Khan
mesh_terms: D001724:Birth Weight; D006801:Humans; D007226:Infant Mortality; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D007232:Infant, Newborn, Diseases / Q000401:mortality*; D016013:Likelihood Functions; D011379:Prognosis; D012680:Sensitivity and Specificity; D047929:Term Birth
keywords: Fetal growth restriction; low birthweight; neonatal morbidity; neonatal mortality; systematic review