Sleeping and waking state development in preterm infants.
BACKGROUND: Most studies of sleep-wake states of preterm infants have been cross-sectional. Thus, the extent to which sleep-wake development occurs within individuals and how environmental factors affect the development of sleeping and waking is unclear. AIMS: This study examined the development of sleeping and waking during the preterm and early post-term periods and the effects of infant health and environmental characteristics. DESIGN: Longitudinal, descriptive design. PARTICIPANTS: 134 preterm infants at high risk for developmental problems because of birthweights under 1500 g or mechanical ventilation. OUTCOME MEASURES: Weekly 2-h behavioral observations were conducted from the time infants were no longer critically ill until 43 weeks post-conceptional age or discharge. A single follow-up observation was conducted 1-3 months later. RESULTS: Active sleep, large body movements and the percent of no REM during active sleep decreased with age, and quiet waking, active waking, quiet sleep and regularity of respiration in active sleep and quiet sleep increased. The state of sleep-wake transition increased until 40 weeks and then decreased after 43 weeks CA. Negative facial expressions showed a quadratic decrease over age. Active waking, active sleep, negative facial expressions and quiet sleep regularity showed a change of development after term. Infant characteristics, illness severity and medical treatments, the handling due to performing an EEG and hospital had only minor effects. CONCLUSIONS: Significant development of sleeping and waking occurs over the preterm period. Additional research is needed to determine how the change from the hospital to the home environment affects on these developmental trajectories.