Sleep maturation influences cognitive development of preterm toddlers

Abstract

Our recent study on full-term toddlers demonstrated that daytime nap properties affect the distribution ratio between nap and nighttime sleep duration in total sleep time but does not affect the overall total amount of daily sleep time. However, there is still no clear scientific consensus as to whether the ratio between naps and nighttime sleep or just daily total sleep duration itself is more important for healthy child development. In the current study, to gain an answer to this question, we examined the relationship between the sleep properties and the cognitive development of toddlers born prematurely using actigraphy and the Kyoto scale of psychological development (KSPD) test. 101 premature toddlers of approximately 1.5 years of age were recruited for the study. Actigraphy units were attached to their waist with an adjustable elastic belt for 7 consecutive days and a child sleep diary was completed by their parents. In the study, we found no significant correlation between either nap or nighttime sleep duration and cognitive development of the preterm toddlers. In contrast, we found that stable daily wake time was significantly associated with better cognitive development, suggesting that sleep regulation may contribute to the brain maturation of preterm toddlers.

The Impact of Preterm Birth on Sleep through Infancy, Childhood and Adolescence and Its Implications

“…At age two, children born <37 weeks of gestation with higher parent-rated sleep difficulties scores had significantly poorer parent-rated attention (r = −0.32) [56]. In toddlers born <36 weeks of gestation and birthweight < 1500 g, at age 1.5 years, greater variation in wake-up time over seven days was associated with lower cognitive test scores [87]. In a longitudinal study with families of children born <37 weeks of gestation, there was an association between a greater number and duration of parent-reported nocturnal awakenings with atypical motor outcomes assessed on the Denver-II and the Alberta Infant Motor Scale at six months corrected age, but at 12 months corrected age, no such relationships were found [88].…”

Preterm toddlers have low nighttime sleep quality and high daytime activity

“…Preterm and term toddlers of approximately 1.5 years of age were recruited from multiple research facilities; Hokkaido University Hospital (Sapporo, Japan), Sapporo City Hospital (Sapporo, Japan), St. Luke’s International Hospital (Tokyo, Japan), Toho University Hospital (Tokyo, Japan), Japanese Red Cross Medical Center (Tokyo, Japan), Kanazawa University Hospital (Kanazawa, Japan) and Akita University Hospital (Akita, Japan), as previously described 19 , 20 . Inclusion criteria were 1) the absence of chromosomal or other major genetic abnormalities, suspected neuromuscular disorders, intraventricular hemorrhage (> grade 1) or significant chronic lung disease (CLD) for both groups of toddlers, 2) birth weight of less than 1,500 g (very low birth weight) and born at less than 37 gestational weeks for the preterm infants, 3) born at between 37 and 42 gestational weeks for term toddlers.…”

“…For sleep assessment, we used Actigraphs (Micro-mini RC, Ambulatory Monitoring Inc., Ardsley, NY, USA) and sleep diaries, as previously described 19 , 20 . Actigraphs, which are wristwatch-like devices, have been widely used for sleep assessment including that of children.…”

“…Infant circadian sleep patterns of day and nighttime sleep incorporating ultradian rhythms of short periods of sleep start to be established by approximately three months of age 14 . In addition, the biphasic sleep pattern of nap and nighttime sleep among young toddlers is established at the latest by 1.5 years of age, while nap duration gradually decreases until napping ceases by 5 years of age 15 – 20 . In the current study, we investigate the difference in sleep characteristics between preterm and term toddlers in order to confirm whether preterm toddlers have a different sleep development process from that of term toddlers at 1.5 years of age, when their fundamental sleep structure normally takes effect.…”