title: The effect of birthweight on childhood cognitive development in a middle-income country.
abstract: BACKGROUND
  Intra-uterine growth is a powerful predictor of infant mortality and of health, developmental and socioeconomic outcomes in adulthood. The question about whether this relationship is causal rather than driven by unobserved characteristics of low-weight infants is, however, still open. We use twin models to examine the hypothesis that in utero growth has a detrimental impact on cognitive development in childhood.
  
  
  METHODS
  We merge birth registry information on birthweight with standardized Math and Spanish test scores for all fourth graders in Chile to create a prospective data set. Twin fixed-effects models are used to estimate the causal effect of intra-uterine growth on test scores. Fixed-effect estimates are compared with traditional regression results in a cross-section of births to gauge the omitted variable bias emerging from unobserved genetic, maternal and pregnancy-related factors in cross-sectional models.
  
  
  RESULTS
  Birthweight differences within twin pairs have a substantial effect on test scores. A 400-g increase in birthweight results in a 15% standard deviation increase in Math scores. The effect is larger among (estimated) monozygotic than dizygotic pairs, reaching >20% standard deviation. The effect varies across family socioeconomic status. It is strong among disadvantaged families but it nearly disappears among advantaged ones.
  
  
  CONCLUSIONS
  Scarcity of uterine resources resulting in intra-uterine growth restriction has a detrimental effect on cognitive development in childhood. This effect interacts with family socioeconomic status (SES), so that low-SES families reinforce the effect of low birthweight and high-SES families fully compensate for it. Findings are particularly relevant in the developing world, where intra-uterine growth restriction is the main determinant of low birthweight.
authors.affiliation: Department of Sociology, New York University, New York, NY 10012, USA. florencia.torche@nyu.edu
authors.forename: Florencia
authors.initials: F
authors.lastname: Torche
authors.forename: Ghislaine
authors.initials: G
authors.lastname: Echevarría
mesh_terms: D000293:Adolescent; D000328:Adult; D001724:Birth Weight / Q000502:physiology*; D002648:Child; D002677:Chile; D003071:Cognition / Q000502:physiology*; D004521:Educational Measurement; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age; D007802:Language; D008137:Longitudinal Studies; D008297:Male; D008423:Maternal Age; D008433:Mathematics / Q000193:education; D011247:Pregnancy; D012042:Registries; D012044:Regression Analysis; D012959:Socioeconomic Factors; D014429:Twins, Dizygotic / Q000523:psychology* / Q000706:statistics & numerical data*; D014430:Twins, Monozygotic / Q000523:psychology* / Q000706:statistics & numerical data*; D055815:Young Adult