Stability of Bayley Motor Scale scores in the first year of life

Abstract

The purpose of this study was to determine whether Bayley Motor Scale scores were stable in infants during the first year of life, that is, whether each individual infant's score was essentially the same at each of the five test ages. Subjects were 15 low-risk and 8 high-risk infants with Bayley Scales of Infant Development Motor Scale scores at 2, 3, 4, 8, and 12 months. All high-risk and most low-risk infants also had outcome scores at either 24 or 36 months. For the group as a whole, and for all infants with 'normal' outcomes, subjects did not change ranks over the six test ages (ie, high-scoring infants' ranks remained high and low-scoring infants' ranks remained low), but scores varied significantly from test to test. Scores of infants with 'non-normal' outcomes did not vary significantly from test to test. The highest and lowest scores of 75% of the infants with normal outcomes and 57% of the infants with non-normal outcomes differed significantly. Four patterns of variations of Bayley Motor Scale scores over the five test ages of the first year after birth were identified. The first pattern included three infants with the most stable scores. The three remaining patterns were different from each other, but a constant feature of each was a peak at 4 months. Finally, scores at 3 and 8 months were best able to correctly identify outcome. A single Bayley Motor Scale score may not reflect an infant's true abilities; some factor may be inflating scores at age 4 months.