Gestational age, birthweight and the risk of hyperkinetic disorder

Karen Markussen Linnet ^1*, Kirsten Wisborg ¹, Esben Agerbo ², Niels-Jørgen Secher ³, Per Hove Thomsen ⁴ and Tine Brink Henriksen ¹

¹ Perinatal Epidemiology Research Unit, Dept. of Obstetrics and Pediatrics, Aarhus Hospital, Denmark
² National Centre for Register-Based Reseach, Aarhus University, Denmark
³ Dept. of Obstetrics and Gynaecology, Hvidovre Hospital, Copenhagen, Denmark
⁴ Psychiatric Hospital for Children and Adolescents, Aarhus University Hospital, Denmark

^* To whom correspondence should be addressed. E-mail: kmlinnet{at}ki.au.dk.

Accepted 13 April 2006

Abstract

Objectives: To study the association between gestational age and birthweight and the risk of clinically verified hyperkinetic disorder.

Design: A nested case-control study with incidence density sampling.

Setting: Danish longitudinal registers.

Patients: 834 cases and 20,100 controls.

Main outcome measure: Hyperkinetic disorder.

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

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

Keywords: attention-deficit hyperkinetic disorder., birthweight, hyperkinetic disorder, intrauterine growth retardation, preterm delivery

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