Infant sleep and development during the first 8 months of life

During the first months of life, dramatic changes occur in infants’ sleep, with sleep-wake patterns starting to consolidate within the first 6 months of life. Sleep hours usually reduce from 16-17 hours in newborns to 13-14 hours at around 6 months of age, and to 9-11 hours when approaching the first year of life. Moreover, while nighttime sleep gradually increases, with fewer awakenings and longer uninterrupted sleep periods, daytime sleep tends to reduce. Remarkably, research indicates that changes in infant sleep are in interaction with important acquisitions in other domains of child maturation, such as cognitive and language development. In the present study, we aimed to investigate concurrent and longitudinal relations between sleep and development in 156 4-months-old infants and in a subsample of 103 8-months-old infants. Infants’ sleep was assessed through the Brief Infant Sleep Questionnaire (BISQ; Sadeh, 2004), whereas cognitive development was evaluated using the Developmental ProfileTM 3 (Alpern 2007). We also examined infants’ language comprehension through the short form of the MacArthur–Bates Communicative Development Inventories (MCDI; Caselli et al., 2015). Finally, information about infants’ temperament and maternal practices potentially relevant for sleep quality, such as the use of a pacifier at nighttime, co-sleeping and exclusive breastfeeding, was detected. Linear Mixed-Effects Modelling showed that at 4 months of age infants sleeping less both during the day and the night obtained higher scores on the DP-3 Physical subscale (Table 1), extending previous findings (Hauck et al., 2018) and suggesting that the time infants spend sleeping during the 24 hours may be related to the kind of movements they produce. However, this finding did not remain significant four months later. At 8 months of age, the night sleep duration was related to the DP-3 General Development scale and to the Adaptive Behavior subscale (Table 1), whereas the daytime sleep was positively related to the DP-3 Social-Emotional subscale (Table 1). Surprisingly, both the language understanding score and the action and gesture production score of the MCDI were positively related to the number of night awakenings. It may be the case that mothers of infants waking several times during the night may give less reliable responses, likely as a consequence of the sleep deprivation to which they are subjected. However, this aspect merits consideration for further investigation. Finally, we found a negative relationship between the day sleep duration at 4 months and the DP-3 General Development score at 8 months (Table 2) and positive relationships between the time infants spent awake at night at 4 months and (i) the DP-3 Adaptive Behavior subscale and (ii) the MCDI’s number of actions and gestures at 8 months (Table 2). Overall, despite the relatively limited and controversial evidence for longitudinal relationships between sleep and infant development, our results provide support and extend previous findings showing that a better sleep quality is associated with a greater cognitive maturation even at very early ages and point out that healthy sleeping in infants is important for cognitive, physical, and socioemotional development.