Sleep/wake states of preterm infants: stability, developmental change, diurnal variation, and relation with caregiving activity.

Using time-lapse video, we recorded the sleep/wake states of 95 preterm infants, born under 1500 g and cared for in three hospitals, for three 24-hr periods at 33 and 35 weeks conceptional age. The videotapes were scored in 5-min epochs for quiet sleep (QS); active sleep (AS); wakefulness (Wa); bout lengths of QS (QSBL), AS (ASBL), and waking (WaBL); nursing/caregiving periods (Crgv); bout lengths of Crgv (CrgvBL); and time out of the crib (OOC). The infants' sleep showed significant individual differences at each age, over age, and from day to nighttime. They showed developmental changes in QS, AS, Wa, and QSBL. QS and QSBL were positively related to caregiving time; ASBL was related to maternal age; and QS was related to gestational age and birth weight. Thus, very low birth weight preterm infants show marked stability and developmental change in the organization of the sleep/wake states from a very early age, and their states are related to demographic variables as well as temporal measures of caregiving.