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ADHD treatment and diagnosis in relation to children's birth month: Nationwide cohort study from Norway

Øystein Karlstad1, Kari Furu1, Camilla Stoltenberg1,2

  • 11 Norwegian Institute of Public Health, Oslo, Norway.

Scandinavian Journal of Public Health
|May 10, 2017
PubMed

Insights

Children born later in the year, making them youngest in their class, have a higher risk of attention-deficit/hyperactivity disorder (ADHD) diagnosis and treatment. This risk increases with age, particularly in older students.

Area of Science:

  • Pediatric medicine
  • Neurodevelopmental disorders
  • Public health

Background:

  • Studies indicate a link between being the youngest in a grade and increased risk for attention-deficit/hyperactivity disorder (ADHD) diagnosis and treatment.
  • In Norway, children born in December are the youngest in their school grade, as school entry is at age six.
  • This study investigates the association between birth month and ADHD in a large Norwegian cohort.

Purpose of the Study:

  • To examine the association between birth month and the risk of attention-deficit/hyperactivity disorder (ADHD) diagnosis and medication.
  • To assess if the risk of ADHD diagnosis and treatment varies based on a child's birth month and grade level.

Main Methods:

  • Utilized national registers for medication, specialist, and primary healthcare diagnoses for 509,827 children born in Norway (1998-2006).
  • Employed Cox proportional-hazards models to estimate hazard ratios for ADHD by birth month, controlling for socioeconomic factors using sibling analyses.
  • Conducted cross-sectional time-series analyses to evaluate ADHD medication risk by birth month across different school grades.

Main Results:

  • Children born in October-December had a higher prevalence of ADHD medication compared to those born in January-March (Boys: 5.3% vs 3.7%; Girls: 2.2% vs 1.3%).
  • Adjusted hazard ratios for ADHD medication were elevated for children born in late autumn (Boys: 1.4; Girls: 1.8) compared to early spring.
  • Increased risk for ADHD diagnosis and treatment was observed for children born late in the year from grade 3 onwards, with greater disparities in higher grades.

Conclusions:

  • Being the youngest child in a grade is associated with a higher risk of receiving attention-deficit/hyperactivity disorder (ADHD) treatment.
  • The disparity in ADHD treatment risk based on birth month becomes more pronounced in older children.
  • Findings highlight the impact of relative age within a school cohort on ADHD diagnosis and treatment patterns.
Abstract

Keywords:
ADHDAttention-deficit/hyperactivity disorderNorwayepidemiologyimmaturitymedication

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