title: Contribution of brain size to IQ and educational underperformance in extremely preterm adolescents.
abstract: OBJECTIVE
  Extremely preterm (EP) survivors have smaller brains, lower IQ, and worse educational achievement than their term-born peers. The contribution of smaller brain size to the IQ and educational disadvantages of EP is unknown. This study aimed (i) to compare brain volumes from multiple brain tissues and structures between EP-born (< 28 weeks) and term-born (≥ 37 weeks) control adolescents, (ii) to explore the relationships of brain tissue volumes with IQ and basic educational skills and whether this differed by group, and (iii) to explore how much total brain tissue volume explains the underperformance of EP adolescents compared with controls.
  
  
  METHODS
  Longitudinal cohort study of 148 EP and 132 term controls born in Victoria, Australia in 1991-92. At age 18, magnetic resonance imaging-determined brain volumes of multiple tissues and structures were calculated. IQ and educational skills were measured using the Wechsler Abbreviated Scale of Intelligence (WASI) and the Wide Range Achievement Test(WRAT-4), respectively.
  
  
  RESULTS
  Brain volumes were smaller in EP adolescents compared with controls (mean difference [95% confidence interval] of -5.9% [-8.0, -3.7%] for total brain tissue volume). The largest relative differences were noted in the thalamus and hippocampus. The EP group had lower IQs(-11.9 [-15.4, -8.5]), spelling(-8.0 [-11.5, -4.6]), math computation(-10.3 [-13.7, -6.9]) and word reading(-5.6 [-8.8, -2.4]) scores than controls; all p-values<0.001. Volumes of total brain tissue and other brain tissues and structures correlated positively with IQ and educational skills, a relationship that was similar for both the EP and controls. Total brain tissue volume explained between 20-40% of the IQ and educational outcome differences between EP and controls.
  
  
  CONCLUSIONS
  EP adolescents had smaller brain volumes, lower IQs and poorer educational performance than controls. Brain volumes of multiple tissues and structures are related to IQ and educational outcomes. Smaller total brain tissue volume is an important contributor to the cognitive and educational underperformance of adolescents born EP.
authors.affiliation: Neonatal Services, Royal Women's Hospital, Melbourne, Australia ; Victorian Infant Brain Studies, Murdoch Childrens Research Institute, Melbourne, Australia ; Department of Obstetrics & Gynaecology, University of Melbourne, Melbourne, Australia.
authors.forename: Jeanie L Y
authors.initials: JL
authors.lastname: Cheong
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Anderson
authors.forename: Gehan
authors.initials: G
authors.lastname: Roberts
authors.forename: Alice C
authors.initials: AC
authors.lastname: Burnett
authors.forename: Katherine J
authors.initials: KJ
authors.lastname: Lee
authors.forename: Deanne K
authors.initials: DK
authors.lastname: Thompson
authors.forename: Carly
authors.initials: C
authors.lastname: Molloy
authors.forename: Michelle
authors.initials: M
authors.lastname: Wilson-Ching
authors.forename: Alan
authors.initials: A
authors.lastname: Connelly
authors.forename: Marc L
authors.initials: ML
authors.lastname: Seal
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Wood
authors.forename: Lex W
authors.initials: LW
authors.lastname: Doyle
mesh_terms: D000293:Adolescent; D001921:Brain / Q000033:anatomy & histology* / Q000254:growth & development; D015331:Cohort Studies; D005260:Female; D006801:Humans; D062071:Infant, Extremely Premature / Q000254:growth & development; D007231:Infant, Newborn; D007360:Intelligence; D007361:Intelligence Tests; D007858:Learning; D008297:Male; D009929:Organ Size