Relationship between duration of crying/fussy behavior and actigraphic sleep measures in early infancy

ObjectiveThe objective of the study is to understand the relationship between sleep development and crying episodes during early infancy more accurately by longitudinal and objective sleep evaluations.DesignThe study is designed as a prospective longitudinal study of infants in the first 4 months of life.MethodsThis study included 31 healthy term infants. At approximately 4- to 6-week intervals, when the infants were aged 4–6 weeks, 8–10 weeks, and 14–16 weeks, their mothers recorded the duration of crying/fussy behavior of infants in a timetable and attached an actigraph to the infants for 3 days. The relationship between 24-h crying/fussy behavior duration and actigraphic sleep measures was examined from both a cross-sectional (age group) and longitudinal (within-infants) perspective. Interactions with diverse covariates were studied by multiple regression analysis.ResultsA significant correlation was found between 24-h crying/fussy behavior duration and proportion of active sleep in infants at 14–16 weeks and in within-infant relationships. Among potential covariates, gestational age and co-sleeping had a significant impact on proportion of active sleep. Results of multiple regression analysis showed that gestational age and co-sleeping were positively associated with proportion of active sleep, whereas 24-h crying/behavior duration was not associated with proportion of active sleep.ConclusionsSubsiding of early crying and decreasing of proportion of active sleep are parallel phenomena in some infants. However, this association was thought to be attributable to the influence of covariates, including co-sleeping or gestational age. The underlying mechanisms regulating these developmental processes might overlap with one another, as covariates that affect one process could affect the other.