title: Birthweight and the risk of childhood-onset type 1 diabetes:  a meta-analysis of observational studies using individual  patient data.
abstract: OBJECTIVE
  We investigated whether children who are heavier at birth have an increased risk of type 1 diabetes.
  
  
  METHODS
  Relevant studies published before February 2009 were identified from literature searches using MEDLINE, Web of Science and EMBASE. Authors of all studies containing relevant data were contacted and asked to provide individual patient data or conduct pre-specified analyses. Risk estimates of type 1 diabetes by category of birthweight were calculated for each study, before and after adjustment for potential confounders.Meta-analysis techniques were then used to derive combined ORs and investigate heterogeneity between studies.
  
  
  RESULTS
  Data were available for 29 predominantly European studies (five cohort, 24 case-control studies), including 12,807 cases of type 1 diabetes. Overall, studies consistently demonstrated that children with birthweight from 3.5 to 4 kg had an increased risk of diabetes of 6% (OR 1.06 [95% CI 1.01-1.11]; p=0.02) and children with birthweight over 4 kg had an increased risk of 10% (OR 1.10 [95% CI 1.04-1.19]; p=0.003), compared with children weighing 3.0 to 3.5 kg at birth. This corresponded to a linear increase in diabetes risk of 3% per 500 g increase in birthweight (OR 1.03 [95% CI 1.00-1.06]; p=0.03). Adjustments for potential confounders such as gestational age, maternal age, birth order, Caesarean section, breastfeeding and maternal diabetes had little effect on these findings.
  
  
  CONCLUSIONS
  Children who are heavier at birth have a significant and consistent, but relatively small increase in risk of type 1 diabetes.
authors.affiliation: Centre for Public Health, School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast, Grosvenor Road, Belfast BT12 6BJ, UK, c.cardwell@qub.ac.uk
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authors.initials: CR
authors.lastname: Cardwell
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mesh_terms: D000293:Adolescent; D017668:Age of Onset; D001722:Birth Order; D001724:Birth Weight; D002648:Child; D002675:Child, Preschool; D003922:Diabetes Mellitus, Type 1 / Q000453:epidemiology*; D005260:Female; D005865:Gestational Age; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008423:Maternal Age; D011247:Pregnancy; D012307:Risk Factors