title: Maternal age at childbirth and risk for ADHD in offspring: a population-based cohort study.
abstract: BACKGROUND
  Women who give birth at younger ages (e.g. teenage mothers) are more likely to have children who exhibit behaviour problems, such as attention-deficit/hyperactivity disorder (ADHD). However, it is not clear whether young maternal age is causally associated with poor offspring outcomes or confounded by familial factors.
  
  
  METHODS
  The association between early maternal age at childbirth and offspring ADHD was studied using data from Swedish national registers. The sample included all children born in Sweden between 1988 and 2003 (N = 1 495 543), including 30 674 children with ADHD. We used sibling- and cousin-comparisons to control for unmeasured genetic and environmental confounding. Further, we used a children-of-siblings model to quantify the genetic and environmental contribution to the association between maternal age and offspring ADHD.
  
  
  RESULTS
  Maternal age at first birth (MAFB) was associated with offspring ADHD. Teenage childbirth (<20 years) was associated with 78% increased risk of ADHD. The association attenuated in cousin-comparison, suggesting unmeasured familial confounding. The children-of-siblings model indicated that the association between MAFB and ADHD was mainly explained by genetic confounding.
  
  
  CONCLUSIONS
  All children born to mothers who bore their first child early in their reproductive lives were at increased risk of ADHD. The association was mainly explained by genetic factors transmitted from mothers to their offspring that contribute to both age at childbirth and ADHD in offspring. Our results highlight the importance of using family-based designs to understand how early life circumstances affect child development.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden, Department of Psychiatry, University of Oxford, Oxford, UK, Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN, USA and Astrid Lindgren Children's Hospital, Karolinska University Hospital, Stockholm, Sweden Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden, Department of Psychiatry, University of Oxford, Oxford, UK, Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN, USA and Astrid Lindgren Children's Hospital, Karolinska University Hospital, Stockholm, Sweden zheng.chang@ki.se.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Chang
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden, Department of Psychiatry, University of Oxford, Oxford, UK, Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN, USA and Astrid Lindgren Children's Hospital, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Paul
authors.initials: P
authors.lastname: Lichtenstein
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden, Department of Psychiatry, University of Oxford, Oxford, UK, Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN, USA and Astrid Lindgren Children's Hospital, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Brian M
authors.initials: BM
authors.lastname: D'Onofrio
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden, Department of Psychiatry, University of Oxford, Oxford, UK, Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN, USA and Astrid Lindgren Children's Hospital, Karolinska University Hospital, Stockholm, Sweden Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden, Department of Psychiatry, University of Oxford, Oxford, UK, Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN, USA and Astrid Lindgren Children's Hospital, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Catarina
authors.initials: C
authors.lastname: Almqvist
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden, Department of Psychiatry, University of Oxford, Oxford, UK, Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN, USA and Astrid Lindgren Children's Hospital, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Ralf
authors.initials: R
authors.lastname: Kuja-Halkola
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden, Department of Psychiatry, University of Oxford, Oxford, UK, Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN, USA and Astrid Lindgren Children's Hospital, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Arvid
authors.initials: A
authors.lastname: Sjölander
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden, Department of Psychiatry, University of Oxford, Oxford, UK, Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN, USA and Astrid Lindgren Children's Hospital, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Henrik
authors.initials: H
authors.lastname: Larsson
mesh_terms: D000293:Adolescent; D000328:Adult; D001289:Attention Deficit Disorder with Hyperactivity / Q000453:epidemiology* / Q000235:genetics; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008423:Maternal Age; D011247:Pregnancy; D011253:Pregnancy in Adolescence / Q000706:statistics & numerical data*; D016016:Proportional Hazards Models; D035781:Siblings / Q000523:psychology*; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult
keywords: ADHD; family-based design; maternal age