Ultradian and diurnal cyclicity in the sleep states of newborn infants during the first two postnatal days

Abstract

Objective: The purpose of this study was to investigate both ultradian and diurnal cyclicity in the sleep states of newborn fullterm infants during the first 2 postnatal days. Methods: The sleep of 31 healthy newborn infants was recorded continuously throughout the first 2 postnatal days, starting immediately after birth, using an automated Motility Monitoring System (MMS). The MMS consists of a pressure sensitive mattress pad connected to an amplifier and a small 24-h analog recorder. A single channel of analog signals produced by the infant's respiration and body movements was recorded and then scored in 30-s epochs for Active Sleep, Quiet Sleep, Active-Quiet Transition, Sleep-Wake Transition, and Wake. Data Analyses: The 48 h of recording were divided into successive 12-h periods from 07:00 h to 19:00 h (day) and 19:00 h to 07:00 h (night), and all measures were derived for each day and night period. Both cross-sectional and repeated measures analyses were used because all babies were not represented in all day/night periods. Results: Day/night differences in state variables: On both days, there was greater Wakefulness, shorter Quiet Sleep Bout Lengths, shorter Mean Sleep Periods and shorter Longest Sleep Periods during the daytime. On day 1 only, there was less Quiet Sleep, shorter Quiet Sleep Bout Lengths and more Sleep-Wake Transition during the daytime. On day 2, repeated measures analyses revealed two additional day/night differences: less Quiet Sleep and more Sleep-Wake Transition during the daytime. Day/night differences in Quiet Sleep cyclicity: 28 sleep periods met the criteria for analysis of Quiet Sleep cyclicity, and only six of these occurred during the daytime. Seventeen of 28 analyzable sleep periods showed significant Quiet Sleep cyclicity. Only two of these occurred during the daytime. Conclusions: Contrary to the prevailing view of developing sleep rhythms, the results of this study suggest that newborn infants exhibit both ultradian ad diurnal cyclicity in their sleep patterns from the earliest postnatal period.