Table 1

Outcome measures and diagnostic scales used in analysis

Cognitive developmental delay
 Bayley Scales of Infant Development (children <42 months)Score >2 SDs below the mean
 Griffiths Scale of Infant Development
 (children >42 months)
Score >2 SDs below the mean
 McCarthy Scales of Children’s Abilities
 (children >30 months)
Score >1 SDs below the mean
 Stanford-Binet IV Intelligence scale for childrenIQ <80
 Touwen’s testAbove-average number of items rated abnormal in one or more domains
 Wechsler Scale of Preschool and Primary IntelligenceIQ <90
 Wechsler Intelligence Scale for Children—IIIIQ <80; verbal IQ <69
 Developmental assessmentConfirmed diagnosis by developmental paediatrician or paediatric neurologist
 Developmental assessmentDiagnosis confirmed by developmental specialists at 2 years of age
 Medical recordsConfirmed diagnosis recorded in medical history; registry records (ICD-10 codes F84.0, F84.1, F84.5, F84.8 and F84.9)
 Modified checklist for autism in toddlersScored positive for >2 out of 6 critical items OR >3 any items of the total scale
Psychomotor developmental delay
 Ages and Stages Questionnaire>3 SDs from the test mean
 Bayley Scales of Infant Development—Psychomotor Index>2 SDs below the standardised mean for the test
 Touwen’s testDemonstrated dysfunctions in fine motor balance, fine motor functions and coordination of extremities
 Schedule of Growing Skills IIScored as ‘delayed’ in >1 domain of the test
 Developmental assessmentInfant scored >2 negative items (administered by general practitioner or paediatrician); diagnosis of neuromotor deficit confirmed by a trained nurse practitioner; infant failing to sit by 10 months or walk by 18 months
 Health/medical recordsDiagnosis of psychomotor delay recorded in medical records
Language delay
 Ages and Stages Questionnaire>3 SDs from the test mean
 Clinical Evaluation of Language Fundamentals—4th EditionScore <70 in core language domain; score<84 overall
 Learning Accomplishment ProfileBelow-average performance in expressive speech (adjusted for age)
 Comprehensive Language Assessment
 (Peabody Picture Vocabulary Test; Receptive Expressive Emergent Language Scale; Expressive One Word Picture Vocabulary Test or Sequenced Inventory of Communication Development)
Scores/assessment indicate a >6-month delay in age-appropriate language development
 Attention Problems and Hyperactivity ScalesScore >1 SDs from the test mean
 Child Behaviour Checklist >6 positive items on checklist
 Diagnostic and Statistical Manual— IV >5 positive items on checklist
 Medical recordsConfirmed diagnosis in hospital/medical records made by a paediatrician or child psychiatrist
Neonatal seizure
 Medical recordsRecord of seizures during first year; confirmation of neonatal seizure by electroencephalography or diagnosis
Social impairment
 Developmental Assessment
 (Ages and Stages Questionnaire (6 and 18 months); Child Behaviour Checklist (36 months))
Scores dichotomised into ‘normal’ or ‘adverse’ range based on predefined values used by scale, for scales without predefined values cut-off was set at a score >2 SDs outside the test mean
  • ADHD, attention-deficit hyperactivity disorder, ICD-10, International Classification of Diseases, Tenth Revision; SD, standard deviation.