Influence of mothers' nighttime responses on the sleep-wake rhythm of 1-month-old infants.

The purpose of this study was to analyze the influence of the mothers' nighttime responses on the sleep-wake rhythm of their 1-month-old infants. This study used an anonymous self-administered survey questionnaire with 1133 mothers of 1-month-old infants. The questionnaire investigated basic information about the parents, growth environment of infants, mothers' sleep patterns during pregnancy, and infants' sleep patterns at the age of one month. Logistic regression analysis was used to analyze the influence of nighttime responses on the risk of infants sleeping longer during the day than at night. Regarding nighttime response behavior, it was found that immediately picking up 1-month-old infants results in longer sleep during the day than at night (OR 1.616 [1.017 - 2.566], p = 0.042), compared to delaying picking up the infant. It was suggested that the stimulation due to picking up an infant may affect sleep-wake rhythm formation.

Peripartum depression and infant care, sleep and growth.

Peripartum depression is a common, serious complication in mothers. To assess the influence of infant care, sleep and growth on the risk of peripartum depression, 1,271 mothers of healthy one-month-old infants completed comprehensive questionnaires including the Edinburgh Postnatal Depression Scale. Relationships between high depression scores and variables related to infants' care, sleep and growth were assessed adjusting for other variables. High depression scores were found in 233 mothers, which were associated with variables related to infants' care (poor satisfaction with infant care support, p < 0.001; mothers' passive response to night-time fussing, p = 0.001), sleep (dim bedroom lighting, p < 0.05; short sleep duration, p < 0.05) and growth (poor weight gain, p < 0.05), as well as maternal variables (primiparas, p < 0.001; poor income satisfaction, p < 0.001; poor sleep satisfaction, p < 0.001; daytime sleepiness, p = 0.001). Considering the observed association between high depression scores and infants' care, sleep and growth, a multidisciplinary approach accounting for infant care would be required to prevent peripartum depression.

Dependence of nighttime sleep duration in one-month-old infants on alterations in natural and artificial photoperiod.

Human sleep-wake cycles are entrained by both natural and artificial light-dark cycles. However, little is known regarding when and how the photoperiod changes entrain the biological clock after conception. To investigate the dependence of sleep patterns in young infants on the natural and artificial light-dark cycles, 1,302 pairs of one-month-old infants and their mothers were asked to answer a questionnaire. Birth in spring, longer daytime sleep duration, early/regular light-off times, and longer maternal nighttime sleep duration were identified as independent variables for longer infant nighttime sleep duration in both univariate and multivariate analyses. Longer maternal nighttime sleep duration was dependent on shorter naps and early/regular bed times but not on the season. We found that nighttime sleep duration depended on both natural and artificial diurnal photoperiod changes in one-month-old infants. Although sleep patterns of infants mimicked those of their mothers, nighttime sleep duration depended on the season, and was positively associated with daytime sleep duration, only in the infants. These specific variables, which render sleep patterns of the infants different from those of their mothers, might be a clue to reveal the covert acquisition process of mature circadian rhythms after birth.