Ultradian and circadian activity-rest rhythms of preterm neonates comparedto full-term neonates using actigraphic monitoring

During the first weeks of life, preterm neonates show fewer circadian rhyth ms in their physiological parameters than full-term neonates. To determine whether preterm neonates differ in their temporal adaptation to the day-nig ht cycle from full-term neonates at the early age of 1 week, we compared ac tivity-rest behavior of both groups. Activity-rest behavior of 10 neurologi cally healthy preterm neonates (born in 34th to 36th week of gestation) and 10 neurologically healthy full-term neonates (born in 37th to 42nd week of gestation) was monitored longitudinally for 8 successive days in the first 2 weeks of life. Actigraphy was used to register and display time patterns of activity and rest in neonates by using small actometers, which resemble a wristwatch. Nursing/feeding was recorded using the actometer's integrate d event marker button. Recordings for preterm neonates were conducted in th e hospital; recordings for full-term neonates were carried out in the hospi tal and in their homes. In addition to the actigraphic recordings, a standa rdized diary was kept regularly. To assess periodic characteristics, freque ncy components of activity-rest behavior were analyzed using fast Fourier t ransformation (FFT). Amounts of daily sleep time, nightly sleep time, and s leep time during 24h were compared. Nursing/feeding epochs were also analyz ed for 5 preterm and 5 full-term neonates to compare their food intake beha vior. The majority of preterm neonates showed a multitude of ultradian freq uencies in their spectra. In contrast, several full-term neonates showed a distinct circadian frequency. In preterm neonates, average nightly sleep an d average daily sleep of all recorded days were very similar, but after the fourth day of life, only average nightly sleep increased. In full-term neo nates, average nightly and daily sleep time of all recorded days differed b y about lh. Average sleep time during 24h for preterm and full-term neonate s was similar. Preterm neonates showed longer intervals between events of f ood intake than full-term neonates. The circadian peaks in the frequency sp ectra of full-term neonates may indicate the initial adaptation in the firs t week of life to a 24h day. This is in agreement with our results concerni ng the different durations of nightly and daily sleep. The increase in nigh tly sleep time of preterm neonates may be attributed to the progressing ada ptation to a circadian activity-rest pattern.