Mental development of preterm infants during the first year.

Developmental rates and standard scores are examined for 56 infants in 4 gestational age groups by repeated measurements on the mental scale of the Bayley Scales of Infant Development. Rates across the first year of life can be predicted largely by a biological model that assumes equality of development for infants of the same conceptual age. However, standard scores based on biological age are elevated during the early months for the most premature groups, indicating a transient advantage of increased extrauterine life. Scores from 3 to 12 months' biological age are slightly higher for the most premature groups but are consistent within groups, with no special acceleration of the premature.