Development of the sleep and wakefulness rhythm in preterm infants discharged from a neonatal care unit.

The purpose of this study was to investigate the effect of constant light in a neonatal care unit on the development of the sleep-and-wakefulness rhythm in preterm infants. Two groups of infants (57 preterm infants without other complications and 58 healthy term infants) were prospectively studied over infancy by a day-by-day plot method, by which sleep-and-wakefulness states were recorded at home for more than 14 d to compare developmental courses of the sleep-and-wakefulness rhythm between the two groups at corrected and postnatal ages. In the two groups, there were no significant differences in distribution of emergence of periodicity of sleep states and wakeful states, total sleep time, nocturnal sleep time, diurnal sleep time, longest sustained sleep period, and longest sustained wakeful period at the same corrected ages. Moreover, the SD of the time of onset of the longest sustained sleep period of each subject diminished with increase in postconceptional weeks. The results suggest that the development of the sleep-and-wakefulness rhythm in preterm infants is not necessarily retarded if they are discharged from the neonatal care unit under constant light before an infant's innate biologic clock is mature enough to respond to an environmental cycle; rather it depends on their corrected ages.