Bayley Scales of Infant Development

The Bayley Scales of Infant Development are normed, individually administered assessments of cognitive, language and motor development in infants and toddlers. Scores are reported as normed composite scores, with a mean of 100 and an SD of 15.

The assessment requires a trained psychologist or developmental specialist and takes around 30 to 90 minutes. It provides a detailed profile of strengths and weaknesses, which is more informative than a screening tool.

Usage. It is used when a screening test is abnormal, when a detailed developmental profile is needed, and in research and clinical follow up of high risk infants.

Indications. Confirmation of developmental delay, detailed profiling before intervention planning, follow up of preterm infants and infants with neonatal brain injury, and assessment of children with suspected sensory or motor impairment.

Preparation and technique. The infant is assessed in a quiet room, ideally after a feed and nap. Testing includes cognitive, language and motor domains, with items chosen by age. Behaviour during testing is recorded, since attention and cooperation affect performance.

Contraindications and precautions. Acute illness, sleep deprivation and sensory impairment lower the reliability of the assessment. The assessment is adapted or deferred where these apply.

Interpretation.

• Composite scores of 85 to 115 fall within the typical range.
• A composite score below 70 indicates significant delay, approximately two SDs under the mean.
• Scores between 70 and 84 indicate mild delay and warrant follow up.
• Domain profiles show uneven development, which is clinically important even when the overall score is typical.

Causes of a low score. Global developmental delay, cerebral palsy, sensory impairment, language disorder, autism spectrum disorder, prematurity, and environmental factors.

Critical values and findings needing immediate action.

• Regression of previously acquired skills requires urgent medical review.
• A very low score with abnormal neurological signs requires prompt specialist assessment.

Limitations and artefacts. Performance depends on the child's cooperation, and a poor session may underestimate ability. Prematurity requires correction of age, and the correction is applied until about 2 years of age. Scores are not stable across short intervals in very young infants, so repeat assessment is needed before diagnosis.

Follow up tests. Repeat assessment at an interval, neurological examination, audiology and vision assessment, and neuroimaging where a brain abnormality is suspected.

Special groups. Preterm infants require corrected age scoring. Infants with motor impairment may need adapted tasks, and the motor domain is interpreted with that in mind.