title: Cognitive outcome at 24 months is more predictive than at 18 months for IQ at 8-9 years in extremely low birth weight children.
abstract: BACKGROUND
  It is unclear whether developmental assessment later or earlier in childhood is the better predictor of intelligence at 8years of age. This is an important distinction as many clinical trials assess their final outcomes only in early childhood, assuming the results are valid for later childhood cognitive functioning.
  
  
  OBJECTIVE
  To compare the ability of developmental assessment at 18 months with 24 months in predicting general intellectual functioning at 8-9 years of age in extremely low birth weight (ELBW, birthweight<1000 g) children.
  
  
  METHODS
  Cohort study.
  
  
  METHODS
  58 ELBW survivors born during 1997 at the Royal Women's Hospital, Melbourne, Australia.
  
  
  METHODS
  Cognitive assessments at each of 18 months, 24 months (Mental Developmental Index [MDI]) and 8-9 years (Full Scale IQ) of age, corrected for prematurity were compared by regression analysis and by the κ statistic (agreement beyond chance).
  
  
  RESULTS
  Both the 18-month and the 24-month MDI were significantly predictive of Full Scale IQ at 8-9 years, but more so for the 24-month MDI, with 38% of variance explained compared with 34% of variance explained by the 18-month MDI. The 24-month MDI, expressed as categories of severe, moderate, mild or no developmental delay, was more predictive of categories of severe, moderate, mild or no intellectual impairment at 8-9 years (weighted κ=0.43, P<0.001) than was the 18-month MDI (weighted κ=0.35, P=0.001).
  
  
  CONCLUSIONS
  Cognitive assessment at 24 months is superior to cognitive assessment at 18 months in predicting IQ and intellectual impairment at 8-9 years of age in ELBW children.
authors.affiliation: Neonatal Paediatrics, the Royal Women's Hospital, Melbourne, Australia. Laura.DeRooy@stgeorges.nhs.uk
authors.forename: Lex W
authors.initials: LW
authors.lastname: Doyle
authors.forename: Peter G
authors.initials: PG
authors.lastname: Davis
authors.forename: Barbara
authors.initials: B
authors.lastname: Schmidt
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Anderson
mesh_terms: D000367:Age Factors; D001724:Birth Weight / Q000502:physiology; D002648:Child; D002657:Child Development / Q000502:physiology*; D002675:Child, Preschool; D003071:Cognition / Q000502:physiology*; D015331:Cohort Studies; D002658:Developmental Disabilities / Q000175:diagnosis* / Q000503:physiopathology; D005260:Female; D005500:Follow-Up Studies; D005865:Gestational Age; D006801:Humans; D007223:Infant; D052577:Infant, Extremely Low Birth Weight / Q000502:physiology / Q000523:psychology; D007231:Infant, Newborn; D007361:Intelligence Tests; D008297:Male; D011379:Prognosis; D016032:Randomized Controlled Trials as Topic