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Gestational age, birth weight, and the risk of hyperkinetic disorder
  1. K M Linnet1,
  2. K Wisborg1,
  3. E Agerbo2,
  4. N J Secher3,
  5. P H Thomsen4,
  6. T B Henriksen1
  1. 1Perinatal Epidemiology Research Unit, Department of Obstetrics and Pediatrics, Aarhus University Hospital, Denmark
  2. 2National Centre for Register-Based Research, Aarhus University, Denmark
  3. 3Department of Obstetrics and Gynaecology, Hvidovre Hospital, Copenhagen, Denmark
  4. 4Psychiatric Hospital for Children and Adolescents, Aarhus University Hospital, Denmark
  1. Correspondence to:
    Dr K M Linnet
    Perinatal Epidemiology Research Unit, Department of Obstetrics and Pediatrics, Aarhus University Hospital, Skejby, DK-8200 Aarhus N, Denmark; kmlinnet{at}


Aims: To study the association between gestational age and birth weight and the risk of clinically verified hyperkinetic disorder.

Methods: Nested case-control study of 834 cases and 20 100 controls with incidence density sampling.

Results: Compared with children born at term, children born with gestational ages of 34–36 completed weeks had a 70% increased risk of hyperkinetic disorder (rate ratio (RR) 1.7, 95% confidence interval (CI) 1.2 to 2.5). Children with gestational ages below 34 completed weeks had an almost threefold increased risk (RR 2.7, 95% CI 1.8 to 4.1). Children born at term with birth weights of 1500–2499 g had a 90% increased risk of hyperkinetic disorder (RR 1.9, 95% CI 1.2 to 2.9), and children with birth weights of 2500–2999 g had a 50% increased risk (RR 1.5, 95% CI 1.2 to 1.8) compared with children born at term with birth weights above 2999 g. The results were adjusted for socioeconomic status of the parents, family history of psychiatric disorders, conduct disorders, comorbidity, and maternal smoking during pregnancy. Results related to birth weight were unchanged after adjusting for differences in gestational age.

Conclusions: Children born preterm, also close to term, and children born at term with low birth weights (1500–2499 g) have an increased risk of clinically verified hyperkinetic disorder. These findings have important public health perspectives because the majority of preterm babies are born close to term.

  • ADHD, attention–deficit hyperactivity disorder
  • CI, confidence interval
  • DSM-IV, Diagnostic and Statistical Manual of Mental Disorders, 4th edition
  • HKD, hyperkinetic disorder
  • IUGR, intrauterine growth retardation
  • ICD-8, International Classification of Diseases, 8th edition
  • ICD-10, International Classification of Diseases, 10th edition
  • IDA database, Integrated Database for Labour Market Research
  • RR, rate ratio
  • preterm delivery
  • birth weight
  • intrauterine growth retardation
  • hyperkinetic disorder
  • attention-deficit hyperkinetic disorder
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  • Published Online First 5 June 2006

  • Funding: The study was financially supported by The Danish Health Insurance Fund (grant nr. 2000B521), The Augustinusfonden (grant nr. 0-1360), Ronald McDonald Charities and Marie Dorthea and Holger From’s Children’s Foundation, Hans and Nora Buchart Foundation, Dagmar Marshalls Foundation. The National Centre for Register-Based Research is funded by the Danish National Research Foundation.

  • Competing interests: none

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