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 children | IQ <80 |
| Touwen’s test | Above-average number of items rated abnormal in one or more domains |
| Wechsler Scale of Preschool and Primary Intelligence | IQ <90 |
| Wechsler Intelligence Scale for Children—III | IQ <80; verbal IQ <69 |
| Developmental assessment | Confirmed diagnosis by developmental paediatrician or paediatric neurologist |
| Autism/dyspraxia | |
| Developmental assessment | Diagnosis confirmed by developmental specialists at 2 years of age |
| Medical records | Confirmed 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 toddlers | Scored 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 test | Demonstrated dysfunctions in fine motor balance, fine motor functions and coordination of extremities |
| Schedule of Growing Skills II | Scored as ‘delayed’ in >1 domain of the test |
| Developmental assessment | Infant 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 records | Diagnosis 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 Edition | Score <70 in core language domain; score<84 overall |
| Learning Accomplishment Profile | Below-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 |
| ADHD | |
| Attention Problems and Hyperactivity Scales | Score >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 records | Confirmed diagnosis in hospital/medical records made by a paediatrician or child psychiatrist |
| Neonatal seizure | |
| Medical records | Record 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.