title: Brighter children? The association between seasonality of birth and child IQ in a population-based birth cohort.
abstract: Season of birth has repeatedly been found to be a risk indicator for adverse neurodevelopmental outcomes. Several explanations for this finding have been put forward but no conclusion has been reached. In the current study, we explored the role of sociodemographic and biological factors in the association between season of birth and child IQ.
  
  
  
  In a prenatally recruited birth cohort (born in 2002-2006), we examined the association between season of birth and non-verbal IQ at age 6 years among 6034 children. We explored how adjusting for socioeconomic status and maternal IQ, childbirth outcomes, pregnancy vitamin D status, nutritional intake, exposure to infections, and child age relative to peers in class changed the relation between season of birth and child IQ.
  
  
  
  We found that spring birth was associated with lower non-verbal IQ (estimate: more than 1 point; β-1.24 (95% CI -2.31 to -0.17), p=0.02; seasonal trend β-0.40 (95% CI -0.74 to -0.07), p=0.02) than birth in summer. Adjustment for different covariates led to a substantial reduction (-65.0% change, in a seasonal trend analysis) of this association. In particular, sociodemographic factors and maternal IQ (-10.0% and -22.5% change, respectively) contributed.
  
  
  
  Season of birth is an indicator of many underlying factors related to child IQ. The observed effects on IQ were small and therefore not of clinical significance.
authors.affiliation: The Generation R Study Group, Erasmus MC, University Medical Center, Rotterdam, The Netherlands.|Department of Child and Adolescent Psychiatry/Psychology, Erasmus MC, University Medical Center, Rotterdam, The Netherlands.|Department of Obstetrics and Gynecology, Erasmus MC, University Medical Center, Rotterdam, The Netherlands.
authors.forename: Nina H
authors.initials: NH
authors.lastname: Grootendorst-van Mil
authors.affiliation: Department of Obstetrics and Gynecology, Erasmus MC, University Medical Center, Rotterdam, The Netherlands.|Department of Pediatrics, Erasmus MC, University Medical Center, Rotterdam, The Netherlands.
authors.forename: Régine P M
authors.initials: RP
authors.lastname: Steegers-Theunissen
authors.affiliation: Department of Epidemiology, Erasmus MC, University Medical Center, Rotterdam, The Netherlands.
authors.forename: Albert
authors.initials: A
authors.lastname: Hofman
authors.affiliation: The Generation R Study Group, Erasmus MC, University Medical Center, Rotterdam, The Netherlands.|Department of Pediatrics, Erasmus MC, University Medical Center, Rotterdam, The Netherlands.|Department of Epidemiology, Erasmus MC, University Medical Center, Rotterdam, The Netherlands.
authors.forename: Vincent W V
authors.initials: VW
authors.lastname: Jaddoe
authors.affiliation: Department of Child and Adolescent Psychiatry/Psychology, Erasmus MC, University Medical Center, Rotterdam, The Netherlands.
authors.forename: Frank C
authors.initials: FC
authors.lastname: Verhulst
authors.affiliation: Department of Child and Adolescent Psychiatry/Psychology, Erasmus MC, University Medical Center, Rotterdam, The Netherlands.|Department of Epidemiology, Erasmus MC, University Medical Center, Rotterdam, The Netherlands.|Department of Psychiatry, Erasmus MC, University Medical Center, Rotterdam, The Netherlands.
authors.forename: Henning
authors.initials: H
authors.lastname: Tiemeier
mesh_terms: D000328:Adult; D000367:Age Factors; D001724:Birth Weight; D002097:C-Reactive Protein / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D015930:Diet Records; D005260:Female; D005334:Fever / Q000523:psychology; D005492:Folic Acid / Q000097:blood; D005865:Gestational Age; D006801:Humans; D007360:Intelligence; D007361:Intelligence Tests; D009035:Mothers / Q000523:psychology*; D009426:Netherlands; D009752:Nutritional Status; D036801:Parturition / Q000523:psychology*; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000097:blood / Q000523:psychology*; D011297:Prenatal Exposure Delayed Effects / Q000523:psychology*; D011446:Prospective Studies; D012621:Seasons; D012959:Socioeconomic Factors; D014807:Vitamin D / Q000097:blood
chemical_list: D014807:Vitamin D; D002097:C-Reactive Protein; D005492:Folic Acid
keywords: EPIDEMIOLOGY; child; cognition; perinatal; seasonality