Association between sleep behavior and motor development in preterm infants

Dear Editor,

The World Health Organization (WHO) estimates 15 million infants are born preterm every year, equal to more than 1 in 10 live births. Prematurity is the cause of 35% of infants’ deaths, as well as a risk factor for complications such as neurocognitive impairment, auditive and visual deficit.¹

In light of the seriousness of the situation, research plays a key role in improving and reducing prematurity complications. Manacero and Nunes² assessed the relation between sleep disturbances and motor development in preterm infants and its repercussion at 4–5 years, furthering our knowledge in the field. The authors observed a possible relation at 6 months, which was not apparent at 12 months; yet they did present delayed or atypical motor development, which disappeared at 4–5 years.

Firstly, it is worth noting that there is a prominent time gap between 12 months and 4–5 years. Due to the lack of assessment during 3 or 4 years, the interpretation of the results is complex. A more exhaustive and enlarged evaluation throughout time would have provided more information on the premature neonates’ evolution and, thus, allow for a more solid conclusion.

At 6 months, more awakenings, longer awake periods, and lateral position were associated with atypical motor development. Furthermore, with the Alberts Infant Motor Scale (AIMS) the supine position was significantly associated with suspected motor development delay, as was observed for the lateral position. Out of the 40 preterm infants studied, 21 were recorded sleeping in a supine position. These results agree with another study,³ which concluded that supine position was associated with delayed gross motor development at 4 and 6 months and correlated prone position with proper gross motor development at 4 to 10 months. However, at 12–36 months and at 11 to 17 months, there was no association established for the supine and prone positions, respectively.

At 12 months and at 4–5 years, no association was found. This could be a result of the sleep quality improvement when compared to 6 months. Sleep differences between infants born at term and premature infants have been described. Premature infants sleep longer and present a higher number of awakenings yet, when they are corrected to the term gestational age, the sleep-wake cycles are similar to those born at term.⁴ Regardless of the fact that sleep patterns vary after 6 months, it is unknown why at 12 months the infants present delayed motor development.

The following limitations were acknowledged by the authors. Because of the longitudinal nature of this study, some families dropped out of the study before its conclusion. The final sample (n = 36) for comparison at 4–5 years was not enough to be statistically significant. For the study to be statistically significant with a 90% power, a sample of n = 38 would have been needed. Moreover, the tests and scales used for assessing infants at 6 and 12 months differed from those used at 4–5 years. A standard methodology for the correct evaluation of the same characteristics at each determined age would have allowed us to properly compare and observe the evolution.

Another issue to consider is gestational age (GA). The WHO¹ has classified children born preterm as extremely preterm (< 28 weeks of GA), very preterm (28 to < 32 weeks), and moderate to late preterm (32 to < 37 weeks). Sleeping position, gestational age, and low birth weight have been described as factors associated with gross motor development.³ Manacero and Nunes² included very preterm and moderate preterm infants in their study. Therefore, results may differ depending on the GA.

Additionally, time spent at Neonatal Intensive Care Units (NICUs) was not examined. NICUs environment has been described to alter sleep patterns in preterm infants.⁵ Preterm infants with an immature brain, are exposed to several stimuli such as light, noise, and procedures, which can lead to alterations in brain function and structure.⁶

The authors acknowledge that mother-child interaction was a factor that was not taken into account. It has been described that mother-child interaction can have a good effect on sleep patterns. According to literature, maternal voice exposure has a crucial impact on sleep⁵ and the lack of mother-child attachment is prejudicial for brain structure and function.⁶ Skin-to-Skin contact or kangaroo care is a helpful method for establishing parents’ attachment, decreasing infant stress, and organizing sleep patterns which, consequently, helps brain maturation.⁷

In conclusion, this field should continue to be investigated. Evidence suggests that sleep behavior produces complications in neurodevelopment. Although no association between sleep behavior and motor development was identified, further research will be needed to understand the effects of poor sleeping in motor development and compare them with Manacero and Nunes.² study. A wide range of factors has to be kept in mind to obtain reliable and comparable results in further studies. Increasing knowledge in this area could promote risk prevention and minimize long-term outcomes through the implementation of strategies such as maternal voice, parents’ attachment, and Skin-to-Skin contact sleep.

Conflicts of interest

The authors declare no conflict of interest.