Sleep-wake patterns in preterm infants and 6 month's home environment: implications for early cognitive development.

AIMS This study examined the relationship between early organization of sleep-wake states and developmental outcome at 6-month-old premature infants. STUDY DESIGN This was a prospective randomized study that evaluated the sleep-wake states of healthy premature infants in the nursery environment for two successive 72-h periods, at 32 and 36 weeks gestational age. SUBJECTS Thirty-four healthy premature infants. OUTCOME MEASURES Three sleep-wake parameters: percent of quiet sleep, activity level and total amount of sleep, were studied with miniature activity monitors attached to the infant's ankles. The rearing environments of the infants were also assessed at 6 months of age, using the HOME Inventory. Finally, child developmental status was recorded by means of the Mental Development Index (MDI) of the Bayley Scales for Infant Development, at a chronological age of 6 months. RESULTS Lower total time spent in night sleep, higher mean level of night activity level, and a later rich home environment were all predictive of higher Bayley scores (MDI) at a chronological age of 6 months. Regression analysis indicated that early biological maturity was more strongly related to the child's developmental status than later home environment, although both contributed to the prediction. CONCLUSIONS These results suggest that biological factors may be significant predictors early in development, whereas the impact of environmental influences increases with development.