THE EARLY MATURATION OF THE CIRCADIAN SYSTEM IN NEWBORNS

The time of maturation of the circadian periodicity in humans has been differently considered. The present study aimed to investigate the ex istence of rhythmic variations in the body temperature of healthy full -term infants just after birth. We studied 19 healthy term newborns, n ursed in their cribs at environment temperature of 25-degrees-C and mo derately dimmed artificial lighting during the night. Continuous recor ding of body temperature was performed with a solid memory recorder (F iamarker) connected to a disposable rectal probe, during the first thr ee days of life. Data were analyzed by means of single and mean cosino r methods and spectral analysis. All the newborns, except two, demonst rated a statistically significant circadian periodicity of temperature (p < .001). Acrophases were distributed along the 24h since the synch ronization to environment was not yet completed. A clear ultradian flu ctuation of body temperature was observed in all 19 newborns with an u nexpected fall of temperature every three-four hours. Our data show th at the maturation of the circadian system is probably almost complete in newborns, but the adjustment to the new environment can be expected in the subsequent weeks of life.