高倉 佐和

An infant's circadian sleep-wake rhythm is established during the first three months after birth. It is crucial to identify how entrainment factors, such as maternal behavioural influences, feeding conditions, and others, contribute to the infant's obtaining circadian rhythm. This study examined the influence of feeding method on the mother's rhythm and on the development of her infant's circadian rest-activity rhythm. The subjects were 24 healthy primiparas (mean age, 29.8) and their full-term infants. We retrospectively divided the subjects into two groups based on feeding method (breastfeeding, 17; mixed-feeding, 7). Actographic recordings for the infants and their mothers were made over 3-5 consecutive days during the 2nd-3rd week, the 6th week, and the 12th week. First, we calculated the mean values of the autocorrelograms from the autocorrelation coefficients and calculated their statistical significance to see their rhythmicity for all the mothers and their infants at each of the periods. Second, we evaluated the mean values of the autocorrelograms to see statistical differences between the feeding methods. For the breastfed infants, the mean values of the autocorrelograms at 24-h for the 6th week were significant. However, the mean values for the mixed-fed infants were unclear. At the 12th week, the mean values of the autocorrelograms at 24-h for both groups of infants were significant. The mean value for the breastfeeding mothers at 24-h was significantly larger than that for the mixed-feeding mothers. In conclusion, the breastfeeding mothers contributed more to their infants achieving circadian rhythm than did the mixed-feeding mothers.

Some infants show a free-running rhythm in their rest-activity. We do not know why, nor do we know exactly what the entrainment factors are for the development of the normal 24-h rest-activity rhythm. Actigraphic recordings on 10 primiparae during late pregnancy and these mothers and their infants during the 2nd, 6th, and 12th wks after birth were made over 3-5 continuous days to investigate maternal and infant entrainment. One infant showed a free-running rest-activity circadian rhythm. In late pregnancy, the period in the autocorrelogram of the mother with the free-running infant was longer than the significant period of the mean autocorrelogram of the mothers with non-free-running infants. The finding of this study indicates the free-running rhythm of infant is not reset by maternal entrainment factors.