[Emergence of circadian rhythms in infants before and after birth: evidence for variations by parental influence]

Organisms have developed endogenous mechanisms for keeping track of time which allow them to adjust to environmental changes. Entrainment of endogenous rhythms to the day-night cycle is of elementary importance for the regulation of physiological processes. How environmental changes influence the manifestation of circadian rhythms during intrauterine and extrauterine growth depend on complex networking of molecular, physiological and sensory mechanisms. This work reports on development of circadian rhythms in the infant, with particular emphasis on the roles of times cues to which the infant is exposed.

Activity data of 12 families were continuously recorded during the first 4 months after birth using non-invasive actigraphs. Recordings of parental activity started at the 3rd trimester of pregnancy. Time series analysis was used to investigate the periodic structure of the data. In addition, we review the literature on the ontogenesis of circadian rhythms in humans.

During the 3rd trimester, daily variation of physiological functions in the fetus showed a high degree of correspondence with maternal circadian rhythms. Early behaviour of most infants was highly variable between individuals but could be assigned to different entrainment patterns. Good correspondence of mother-infant activity patterns during the early postnatal period, when the infant was not yet entrained to the day-night-cycle, was correlated with the rapid development of an entrained daily pattern in the infant a few weeks later.

Understanding the emergence of periodic structures at physiological and behavioural level during human ontogenesis will be an asset in the successful intervention and treatment during neonatal care.