title: Influence of birth weight on differences in infant mortality by social class and legitimacy.
abstract: OBJECTIVE
  To investigate the influence of birth weight on the pronounced social class differences in infant mortality in Britain.
  
  
  METHODS
  Analysis of routine data on births and infant deaths.
  
  
  METHODS
  England and Wales.
  
  
  METHODS
  All live births and infant deaths, 1983-5.
  
  
  METHODS
  Mortality in infants by social class, birth weight, and legitimacy according to birth and death certificates.
  
  
  RESULTS
  Neonatal and postneonatal mortality (deaths/1000 births) increased with social class. Neonatal and postneonatal mortality was 4.2/1000 and 2.3/1000 respectively for social class I and 6.8/1000 and 5.6/1000 respectively for social class V. Mortality was lower among births registered within marriage (postneonatal 3.5/1000; neonatal 5.2/1000) than among those jointly registered outside marriage (5.1/1000; 6.4/1000); mortality was highest in those solely registered outside marriage (7.2/1000; 7.0/1000). For neonatal mortality the effect of social class varied with birth weight. Social class had little effect on neonatal mortality in low birthweight babies and increasing effect in heavier babies. For postneonatal mortality the effect of social class was similar for all birth weights and was almost as steep as for all birth weights combined.
  
  
  CONCLUSIONS
  Birth weight mediates little of the effect of social class on postneonatal mortality.
authors.affiliation: Department of Epidemiology and Population Sciences, London School of Hygiene and Tropical Medicine.
authors.forename: D A
authors.initials: DA
authors.lastname: Leon
mesh_terms: D001724:Birth Weight; D004739:England / Q000453:epidemiology; D006801:Humans; D007086:Illegitimacy; D007226:Infant Mortality; D007231:Infant, Newborn; D012307:Risk Factors; D012923:Social Class; D014852:Wales / Q000453:epidemiology