The Specific Test of Early Infant Motor Performance (STEP): A Short,Novel Infant Motor Test at 12 Weeks That Correlates With Bayley Motor Scores at 12 Months

SIGNIFICANCE Premature infants with normal cranial ultrasounds remain at risk for later motor delays, which go undetected in early infancy. Of the 12% to 16% of children with developmental delay, only half will be identified by the time they enter kindergarten. The Test of Infant Motor Performance (TIMP) is the current gold standard assessment, but it is rarely used by pediatricians during well-child visits due to a lack of time and the special training required. A short, standardized screening test administered to infants in the first months of life would target early intervention to those most at risk.

INNOVATION A short infant motor assessment that could be administered to all at-risk infants before discharge from the nursery is a novel concept. Current infant motor assessments are long, need specific training, and are simply not used by pediatricians. Less than 20% of pediatricians use a standardized developmental screening tool, and only 57% of pediatricians use one if parents raise concerns about their child.

METHOD Specific aims were to evaluate psychometric properties of the Specific Test of Early infant motor Performance (STEP) through factor analysis and to test the STEP against current validated infant motor skills assessments at term correct age (CA), 12-wk CA, and 12-mo CA. To accomplish this, the researchers used a secondary analysis of existing video-recorded motor tests at term CA, 12-wk CA, and 12-mo CA. Participants included a cohort of 22 preterm infants (24- to 35-wk gestation) with no structural central nervous system abnormality. The setting took place in an infant motor laboratory.

Measures were STEP scored from existing video-recorded motor tests of TIMP at term CA and 12-wk CA. The Bayley Scales of Infant and Toddler Development–Third Edition (Bayley–III) at 12-mo CA (Bayley–III subscale scores ≤ 8 = low/below average) also were used.

Pearson’s correlational coefficient was used to relate TIMP, Bayley–III, and STEP scores. Exploratory factor analysis (EFA) was used to identify latent constructs of STEP. Logistic regression, using EFA scores, was performed to predict dichotomized Bayley–III outcome. Sensitivity and specificity of EFA STEP scores were evaluated using predictive outcomes versus actual outcomes. A drop-one-predict evaluation was used to assess external validity.

RESULTS EFA revealed a pattern of relationships between STEP items and head, arm, and trunk movements. The ability of the STEP to predict Bayley motor outcomes with EFA scores was as follows: sensitivity = 1.00, and specificity = 0.91. The ability to prospectively identify at-risk infants (external validity) was as follows: sensitivity = 0.75, and specificity = 0.82. STEP correlated with TIMP scores at term CA (r = .06, p = .003) and 12-wk CA (r = .79, p < .001); STEP also correlated with the change in TIMP scores from term CA to 12-wk CA (r = .46, p = .035), indicating that it might be a short, specific surrogate measure of a much longer motor test. STEP at 12-wk CA correlated better with Bayley–III total motor score than with the TIMP (STEP: r = .68, p = .001; TIMP: r = .44, p = .061).

CONCLUSION This is a preliminary analysis of the psychometric properties of the STEP. Validation of the STEP as a clinically useful infant motor assessment requires further analysis. Early head movements as well as patterns of standing, kicking, and visual responses may be sensitive enough to discriminate differences between typical and at-risk infants. Although the numbers are small, the strength of the associations is encouraging and provides strong pilot data and proof of concept for future validity of the STEP assessment.

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