Longitudinal study of infant's sleep-wake rhythm and the influences on the development of their babies' sleep behaviors.

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Only a few studies have researched the development of infants' sleep rhythm in connection with the mothers' sleep-wake behavior. The longitudinal study was conducted to understand the influence on sleep rhythm of infants in accordance with their mothers' sleep behavior, using an actimeter worn on the non-dominant wrist and a sleep log. Sleep logs of the 16 mother-baby pairs recorded consecutively from the delivery day to the 56th weeks after birth were analyzed. Actigraphic recording for the 3 mother-baby pairs were made over 2continuous days during 3rd,6th,9th,15th,23rd,34th, and 55th weeks after birth. A 24-h on a mean autocorrelogram of the infants' sleep rhythms was detected at the 3rd week. The infants' circadian rest-activity rhythm already existed in the 3^<rd>d week. The amplitude of this 24-h peak gradually increased from the 5th to 10th week. This may be useful as an index of the development of infants' circadian sleep rhythm. An about 12-h peak was also observed at 6th week. This 12-h peak was thought to be a semi-circadian rhythm. Regarding the mothers, the mean amplitude of the circadian rhythms decreased markedly from the delivery to 3rd postpartum day, and tended to increase after that. This meant that the mothers' circadian rhythm at the 3rd week was influenced by their interrupted sleep at night to take care of their infants. Sleep onset and wake onset of mothers and their infants showed similar changes at night from the first to the 55th weeks after birth, but the sleep onset and wake onset of the mother-baby pairs in primiparae was late than those of mother-baby pairs in multiparae. These results may indicate that the parity of the mothers have modification effects in the development of infants' sleep rhythm. The mother-infant synchronization is probably the first factor in the entrainment of infants' circadian sleep/ wake rhythm.