Cyclicity of neonatal sleep behaviors at 25 to 30 weeks' postconceptional age

Previous sleep studies of preterm neonates describe the rudimentary expression of sleep state cyclicity after 30 wk postconceptional age (PCA), with stability over multiple cycles only after 36 wk PCA. The research objective for this study was to determine whether sleep state cyclicity was expressed in neonates of 25-30 wk PCA, using two criteria for state identification. Our neonatal sleep consortium includes a total cohort of 359 children who were healthy and medically ill neonates who were recruited from three obstetric-neonatal services and received multiple-hour EEG sleep studies. A subset of the 33 youngest preterm infants were selected to evaluate the first of serial 2- to 3-h EEG-sleep recordings to assess the presence of sleep state cyclicity. One neonatal neurophysiologist visually assigned EEG-sleep characteristics for each record. Rapid eye movement (REM) counts and EEG discontinuity were specifically chosen to assess whether sleep cyclicity was expressed. A combined measure of REM and EEG discontinuity were used in an autocovariance analysis to assess cycling and mean cycle duration. A mean cycle duration of 68 +/- 19 min with a range of 37-100 min was determined from the REM-EEG discontinuity state for 24 neonates. The remaining nine infants had absent or poor sleep cyclicity. Sleep state cyclicity is expressed for a majority of neonates between 25 and 30 wk PCA, reflecting an ultradian biologic rhythm during the early perinatal stage of brain development.