Birth order and childhood type 1 diabetes risk: A pooled analysis of 31 observational studies

Chris R. Cardwell, Lars C. Stene, Geir Joner, Max K. Bulsara, Ondrej Cinek, Joachim Rosenbauer, Johnny Ludvigsson, Jannet Svensson, Michael J. Goldacre, Thomas Waldhoer, Przemystawa Jarosz-Chobot, Suely GA Gimeno, Lee Ming Chuang, Christine L. Roberts, Roger C. Parslow, Emma JK Wadsworth, Amanda Chetwynd, Girts Brigis, Brone Urbonaite, Sandra ŠipetićEdith Schober, Gabriele Devoti, Constantin Ionescu-Tirgoviste, Carine E. de Beaufort, Denka Stoyanov, Karsten Buschard, Katja Radon, Christopher Glatthaar, Chris C. Patterson

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Background: The incidence rates of childhood onset type 1 diabetes are almost universally increasing across the globe but the aetiology of the disease remains largely unknown. We investigated whether birth order is associated with the risk of childhood diabetes by performing a pooled analysis of previous studies. Methods: Relevant studies published before January 2010 were identified from MEDLINE, Web of Science and EMBASE. Authors of studies provided individual patient data or conducted pre-specified analyses. Meta-analysis techniques were used to derive combined odds ratios (ORs), before and after adjustment for confounders, and investigate heterogeneity. Results: Data were available for 6 cohort and 25 case-control studies, including 11 955 cases of type 1 diabetes. Overall, there was no evidence of an association prior to adjustment for confounders. After adjustment for maternal age at birth and other confounders, a reduction in the risk of diabetes in second-or later born children became apparent [fully adjusted OR=0.90 95% confidence interval (CI) 0.83-0.98; P=0.02] but this association varied markedly between studies (I2=67%). An a priori subgroup analysis showed that the association was stronger and more consistent in children <5years of age (n=25 studies, maternal age adjusted OR=0.84 95% CI 0.75, 0.93; I2=23%). Conclusion: Although the association varied between studies, there was some evidence of a lower risk of childhood onset type 1 diabetes with increasing birth order, particularly in children aged <5 years. This finding could reflect increased exposure to infections in early life in later born children. Published by Oxford University Press on behalf of the International Epidemiological Association

Original languageEnglish
Article numberdyq207
Pages (from-to)363-374
Number of pages12
JournalInternational Journal of Epidemiology
Issue number2
Publication statusPublished - Apr 2011


  • Birth order
  • Diabetes mellitus
  • Epidemiology
  • Meta-analysis
  • Type 1

Field of Science*

  • 3.3 Health sciences
  • 3.2 Clinical medicine

Publication Type*

  • 1.1. Scientific article indexed in Web of Science and/or Scopus database


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