Authors

  1. Head, Lauren M. BSN

Abstract

Preterm birth is associated with long-term deficits in executive functioning and cognitive performance. As advances in neonatal care enable more preterm infants to survive, development of strategies to address high rates of neurodevelopmental disabilities and poor academic achievement in preterm infants are crucial. Evidence suggests that infants' brains are plastic in nature and, therefore, can be shaped by the environment. Kangaroo care has become popularized as a means of modifying the stress of the NICU environment. However, few studies have examined whether kangaroo care affects neurodevelopmental outcomes in preterm infants. This review examined available literature that investigated the effect of kangaroo care on cognition in preterm infants. Current evidence suggests that short-term benefits of kangaroo care are associated with improved neurodevelopment. However, few studies have examined the long-term impact of kangaroo care on cognitive outcomes in preterm infants. To address neurological disparities in children born preterm, research using kangaroo care as a strategy to improve neurodevelopment in preterm infants is warranted.

 

Article Content

Preterm birth, defined by the World Health Organization as birth occurring at less than 37 completed gestational weeks, is a key determinant of newborn survival and later health outcomes for infants that do survive.1 Annually, nearly 15 million babies, or 11.8%, are born preterm worldwide and 1 million of these babies die within the first month of life.1 Despite improvements in maternal and infant health, preterm birth is increasing in almost every country where data are available.1 Preterm birth in the United States has increased by 36% in the past 25 years, with nearly half a million infants born preterm in 2012,1 costing the United States health system approximately $26 billion dollars a year.2 Although advances in neonatal care have resulted in improved survival for preterm infants, the 40% prevalence of neurodevelopmental disabilities in surviving children represents a growing public health concern.3 Shortened gestation predisposes preterm infants to a variety of health, behavioral, and developmental problems as evidenced by epidemiological studies that show higher rates of chronic disease, cognitive deficits, poor educational achievement and attainment, and disabilities among individuals born preterm.2 These adverse outcomes are most marked among individuals born extremely preterm (<28 weeks) and very preterm (28-32 weeks), but increasing evidence demonstrates that all preterm infants regardless of gestational age, including late preterm infants (34-36 weeks), are at increased risk for poor developmental sequelae.4

 

Preterm birth interrupts rapid growth in the brain that occurs in the third trimester.5 Brain volume increases nearly 3-fold between gestational age of 29 weeks and 40 weeks.6 In other words, infants born less than 29 weeks have only one-third the brain volume as term infants. Remarkably, infants born at 35 weeks, who have historically been considered low risk, have only two-thirds the brain volume compared with infants born only 5 weeks later.6 Studies have suggested that decreased brain volume persists throughout childhood and correlates with measures of intelligence and executive functioning.7 Because the prefrontal cortex, which governs executive functions, matures during the last 2 months of gestation, preterm infants are particularly vulnerable to deficits in executive control.5 Executive functioning refers to multiple cognitive processes that control thoughts and behaviors, including working memory, planning and organization, attention, response inhibition, and self-regulation.8 These processes are responsible for cognitive performance, behavior, emotional control, and social interaction, all of which underlie educational achievement.

 

Neurodevelopment of preterm infants is subsequently at risk because the immature preterm brain is not equipped to process stimuli that are present within the context of the neonatal intensive care unit (NICU). As a result, adverse NICU stimuli, including lights, noise, frequent handling, and painful procedures, have been found to negatively influence neurological outcomes.5 This evidence is supported by the theory of brain plasticity, which postulates that the brain can reorganize and develop in response to changes in environmental stimuli, or is plastic.9 As shown in Figure 1, the environment affects brain development by stimulating the release of neurochemicals, which guide the formation, strengthening, and deletion of synaptic connections either directly or indirectly through influencing gene expression.9 Plasticity is most robust during the first year of life, when neural circuitry is undifferentiated and formation and deletion of synapses are occurring at a rapid rate.5,9 Given that the NICU environment may affect neurodevelopmental outcomes, the preterm infant's brain appears to be plastic in nature and thus their neurodevelopment may be modifiable by altering the NICU experience.

  
Figure 1 - Click to enlarge in new windowFigure 1. Conceptual framework for brain plasticity.

Recently, kangaroo care has become popularized as a strategy in the NICU to promote parent-infant attachment while regulating infants' physiology and behavior. Kangaroo care consists of placing the preterm infant, once stable, in an upright position with direct skin-to-skin contact on the parent's chest.10 Infants are exclusively breast-fed, although some preterm infants require some form of supplementation.10 A robust line of evidence suggests that many short-term benefits from kangaroo care exist for the preterm infant, including enhanced mother-infant attachment,11-13 improved sleep-wake cycles,12,14,15 higher rates of breast-feeding,16 more stable heart and respiratory patterns,12,14 and decreased response to pain.17,18 However, it is less well known whether kangaroo care has lasting effects on the preterm infant beyond infancy, particularly in regard to cognitive development. Because the application of kangaroo care coincides with timing of rapid brain growth and myelination, kangaroo care may affect neurodevelopmental outcomes. This article seeks to review available literature that addresses the effects of kangaroo care on the neurodevelopment of preterm infants.

 

REVIEW OF THE LITERATURE

A comprehensive literature search was conducted using the databases PubMed, Web of Science, and Cumulative Index to Nursing and Allied Health Literature in order to review available literature involving the effect of kangaroo care on the executive functioning and cognitive performance of preterm infants throughout childhood. Key words included "preterm or premature," "cognition or test scores or academic achievement or executive function or brain development," and "kangaroo care or skin-to-skin contact." The searches were limited to articles written in English and published between 2003 and 2013. Additional sources were identified from the reference lists of selected articles. Literature reviewed included primary research articles, meta-analyses, and reviews.

 

KANGAROO CARE'S SHORT-TERM BENEFITS INFLUENCE ON BRAIN DEVELOPMENT

Infant stress

Preterm infants are at risk for elevated stress as the result of exposure to adverse environmental stimuli in the NICU. Repetitive stress may affect the structural trajectory of preterm infant's brain development and influence subsequent neurodevelopmental outcomes through abnormal production and release of neurohormones.19-21 Greater neonatal pain, as measured through number of needle sticks, has been found to be associated with altered functional connectivity and decreased subcortical white and gray matter at term equivalency22 as well as with a thinner cortex in middle childhood23 even after adjusting for clinical factors and gestational age in preterm infants of 32 weeks or less. Similarly, studies found a correlation between the number of needle sticks and cognitive outcomes on the Bayley Mental Developmental Index in children born 32 weeks or less at 8 months and 18 months.21 Moreover, a randomized controlled trial found that NICU noise exposure was directly associated with poorer scores on the Bayley Mental Developmental Index in very low-birth-weight (<1501 g) infants at 18 to 22 months.24

 

Given this evidence, it seems logical that modulating the stressful environment would result in less cognitive impairment. Kangaroo care may decrease exposure to noxious stimuli and decrease stress responses. Studies comparing the effect of kangaroo care on the response to heel sticks in preterm infants 28 to 33 weeks and 32 to 37 weeks found that heart rate change in response to heel sticks was smaller and recovery time to baseline heart rate was faster in infants who received kangaroo care.17,18 Furthermore, scores on the Premature Infant Pain Profile, which measures heart rate change, oxygen saturation, and behavioral cues, were significantly lower for kangaroo care infants, suggesting that kangaroo care mediates response to stressful procedures.17

 

Maternal-infant attachment

The regulation theory of Schore25 suggests that maternal-infant interactions shape the development of an infant's response to stress. However, development of a positive parental-infant relationship within the context of the NICU is inundated with challenges. Typically, the preterm infant remains in an isolette and is handled only at certain times of the day. This restricts both parental involvement and the physical closeness of mother and infant.

 

Disrupted early maternal-infant interactions influence secure infant attachments, which may affect long-term cognition.26 Evidence suggests that infants who are insecurely attached have increased neurodevelopmental delays compared with those with secure attachments.26 The regulation theory of Schore25 suggests that positive maternal-infant interactions have the potential to change neurobiological processes and influence brain structure and function.27 However, quality of interactions between mother and child seems to be important for this effect. A study showed that the number of postpartum depression symptoms were associated negatively with the quality of maternal interaction with the preterm infant (<=32 weeks), assessed by the parent-child early relational assessment method.28 Unfortunately, parents of preterm infants have been found to report higher rates of stress, anxiety, and depression than parents of term infants.11,29 This poor psychological functioning has been suggested to have long-term impacts on child behavior and development.30 For example, cortisol levels are higher in preterm infants when cared for by depressed mothers, suggesting that maternal stress influences stress of the infant.31

 

Kangaroo care shortens the period for which parent-infant interaction is restricted. Studies demonstrate that kangaroo care facilitates parent-infant attachment,11,12 increases feelings of parental competence,14 and decreases the prevalence of maternal depression and anxiety.12,32 In a study that assessed attachment using a structured interview, attachment and caregiving satisfaction was greater for the kangaroo mothers than that for the control group.33 Kangaroo mothers had lower scores on depression scales at 1 week and 1 month postpartum and lower levels of salivary cortisol in the first month postpartum relative to the control group.34

 

Infant physiology, sleep, and feeding

Although premature infants exhibit disorganized sleep-wake patterns because of brain immaturity and unestablished circadian rhythms, degree of disorganized sleep cycles varies among preterm infants.35 Infants whose sleep-wake cycles are characterized mainly by shifts between quiet sleep and calm, but alert, wakeful states exhibit better cognitive development and greater executive competencies at 6, 12, and 24 months and 5 years than infants whose sleep-wake cycles are characterized by shifts between active sleep and a state of high arousal.35 Furthermore, more organized sleep patterns are associated with increased functional connectivity and neuromaturation.15 In addition, chronic physiologic instability, as assessed by cumulative daily score for Neonatal Acute Physiology, is associated with poor Bayley Scale of Infant Development in extremely preterm infants at 1 to 3 years of age, independent of gestational age.36

 

Preterm infants who received kangaroo care have been shown to sleep longer and have better quality sleep relative to preterm infants who received standard of care.14,36 In a study that assessed 8 infants at 32 weeks and 40 weeks postmenstrual age, kangaroo care, provided for 1.5 hours per day for 8 weeks, appeared to accelerate sleep state organization and maturation when compared with the nonkangaroo cohort.15 During kangaroo care, infants have lower and more stable heart rates, maintain body temperature, and experience improved oxygenation and gas exchange.14 Furthermore, concentrations of hormones that influence synaptic plasticity, such as brain growth promoting factor and oxytocin, are increased in preterm infants who receive kangaroo care.11 These results suggest that kangaroo care mediates the stress of the extrauterine environment and may promote synaptic plasticity.

 

Premature infants receiving kangaroo care latch and feed better than controls and have increased measures of breast-feeding, including longer breast-feeding duration beyond 40 weeks of postmenstrual age and higher rates of exclusive breast-feeding.14,16 Furthermore, volume of maternal breast milk is correlated with kangaroo care.37 Breast-fed infants, regardless of gestational age, have higher white matter in their prefrontal cortex38 and have significantly increased cortical thickness relative to bottle-fed infants.32 Likewise, breast-feeding is associated with a higher intelligence quotient.32

 

Taken together, kangaroo care may promote neurodevelopment through multiple modalities, including decreased infant and maternal stress, regulation of physiological parameters and sleep-wake cycle, and promotion of breast-feeding.

 

KANGAROO CARE AND LONG-TERM NEURODEVELOPMENTAL OUTCOMES

As shown in Table 1, short-term benefits of kangaroo care are well documented. Studies have demonstrated that these short-term benefits are associated with neurodevelopment independent of kangaroo care. Few studies have directly explored whether kangaroo care affects neurodevelopmental outcomes, all of which were conducted in Columbia. Two studies were identified that compared cognitive performance of infants receiving kangaroo care with control groups.10,12 One randomized controlled trial consisting of 336 preterm infants with a birth weight of 1800 g or less used the Griffiths test, which assesses locomotor, social, hearing, speech, eye-hand coordination, and practical reasoning skills.10 For each skill, subscale intelligence quotient is developed independently and then combined to obtain an overall intelligence quotient score.10 The infants randomized to the kangaroo group were maintained in this position for 24 hours per day until the infant began to resist this position, which usually occurred around 37 weeks postmenstrual age.10 Preterm infants who received kangaroo care were found to score 3.7 points higher on the Griffiths test at 12 months corrected age relative to controls (P < .02).10 While the score difference was statistically significant, it was not clinically important. To examine factors that influenced the effect of kangaroo care on cognitive development, variables including birth status and results of the International Neurological Battery at 6 months of corrected age were added into the analysis.10 The International Neurological Battery assesses gross motor development on the basis of 20 different measures and categorizes the neuromotor function of infants as normal, transient-abnormal, or abnormal.10 In high-risk infants, defined as those who needed resuscitation at birth or had either a transient-abnormal or abnormal result on the International Neurological Battery, the difference in Griffiths scores for the kangaroo group was 6.5 and 7 points higher, respectively, and 12.9 points higher in infants who met both these criteria (P < .06).10 These results were clinically important and suggest that kangaroo care affects neurodevelopment of those at high risk for developmental impairments. However, this study did not control for some factors known to promote development, such as measures of breast-feeding and nutritional supplements. As a result, it cannot be determined whether improved performance was truly attributable to kangaroo care.

  
Table 1-a. Summary o... - Click to enlarge in new windowTable 1-a. Summary of kangaroo care benefits

Similarly, significant cognitive differences were observed between kangaroo care and control groups of preterm infants born less than 34 weeks (n = 146).12 This longitudinal study examined the effect of kangaroo care on the Bayley Scales of Infant Development, which consists of developmental play tasks that measure cognitive development, and on the Wechsler Preschool and Primary Scale of Intelligence and the NEPSY (A Developmental Neuropsychological Assessment), which are standardized measurements of overall executive functioning and neuropsychological development.12 The kangaroo group, who received kangaroo care for 1 hour every day for 2 weeks, outperformed the control group on Bayley Scales of Infant Development at 6, 12, and 24 months corrected age (P = .004).12,13 When the same group was assessed at 5 years and 10 years of age (n = 117), the kangaroo group scored better on both the Wechsler Scales and the NEPSY (P = .027).12 Variables controlled for included gender, birth weight, gestational age, parental age and education, socioeconomic status, and medical risk as quantified by the Clinical Risk Index for Babies.12 However, the study is limited by its failure to control for breast-feeding, nutritional supplements, and other developmental interventions. The study is further limited by the recruitment design as the recruitment of the kangaroo group took place in Columbia but recruitment of the control group took place in Israel where kangaroo care is not the standard of care.12 While results suggest that kangaroo care improves cognitive sequelae and executive functioning across infancy into middle childhood, these limitations undermine the reliability of these findings.

  
Table 1-b. Summary o... - Click to enlarge in new windowTable 1-b. Summary of kangaroo care benefits
 
Table 1-c. Summary o... - Click to enlarge in new windowTable 1-c. Summary of kangaroo care benefits

In addition, 1 study evaluated the effect of kangaroo care on long-term cognition in 39 adolescents with a history of preterm birth less than 33 weeks and in 9 adolescents born at term by using transcranial magnetic stimulation.39 Transcranial magnetic stimulation induces a muscle contraction for which speed of conduction and inhibition of muscle contraction can be measured.39 Faster conduction and inhibition speed reflect enhanced connectivity of the corpus callosum and greater myelination.39 The preterm-born adolescents had previously been part of a randomized controlled trial for kangaroo care at birth.39 The kangaroo group received 24 hours of kangaroo care per day for a mean of 28.67 +/- 11.5 days.39 Adolescents who were born preterm and had received kangaroo care had faster conduction and inhibition than those who had not received kangaroo care (P = .029) and did not differ significantly from the term control group.39 Interestingly, speed of conduction was directly associated with the amount of days in kangaroo care, suggesting that a dose response exists for kangaroo care.39 Because breast-feeding rates were similar between kangaroo and control groups, this study suggests that kangaroo care apart from breast-feeding is responsible for cognitive differences.39 As a result, it may be possible that kangaroo care facilitates myelination and synaptic formation. Taken together, these 3 studies suggest that kangaroo care may promote or protect structural brain development and synaptic efficacy.

 

IMPLICATIONS FOR RESEARCH AND PRACTICE

Evidence reveals an inverse relationship between gestational age and executive control.8 Strategies aimed at reducing this neurological disparity are limited. While short-term behavioral, psychological, and physiological benefits of kangaroo care are well documented, few studies have examined whether advantages exist for cognition and executive functioning.

 

Kangaroo care may be an appropriate strategy for improving neurodevelopment for several reasons. First, evidence suggests that early environmental conditions affect neurodevelopment.5 Kangaroo care, which is introduced early in life when neural plasticity is most robust, modifies the stress of the extrauterine environment to minimize the impact of adverse stimuli.17,18 Second, evidence suggests that stress has adverse implications for the preterm infant's developing brain.19-24 Kangaroo care modifies stress through parental-infant interactions,11,12,28,33,34,40 which is reflected in more stable physiologic indicators14,17 and more organized sleep.15 Positive maternal-infant attachment and healthier physiological parameters promote neural formation and connectivity.10,12 Finally, preterm infants exhibit remarkably reduced white matter and cortical gray matter.5 If benefits associated with kangaroo care can affect the connectivity and structure of the brain, kangaroo care may help decrease the anatomical difference in brain structure between preterm-born children and term-born children. Given that structural abnormalities in the brain are associated with deficits in function, improvements in functioning may result.

 

Evidence has suggested that short-term benefits, namely, improved sleep, stability, feeding, stress response, and attachment, all positively affect structural and functional brain development as individual and isolated factors apart from kangaroo care, so it seems likely that kangaroo care could be a promising strategy for either promoting neurodevelopment or preventing further neurological insult. Limited studies support this hypothesis by showing enhanced structural brain development and synaptic efficacy39 as well as better performance on cognitive measures in preterm-born children who received kangaroo care compared to traditional care.10,12 Although results from studies examining the effect of kangaroo care on brain development are consistent, the studies are limited in scope due to flawed methodology and failure to control for factors known to affect neurodevelopmental outcomes. As a result, further research investigating the long-term effect of kangaroo care on cognitive outcomes and executive control is warranted.

 

Future research should encompass all age groups, from infancy to adulthood, to determine whether cognitive and structural benefits observed in the current evidence persist. Kangaroo care may confer early benefits but infants who receive traditional care may catch up later. Therefore, longitudinal analyses of the mother-infant dyad are critical for this research. Examining different domains of executive functioning as well as academic achievement is important to identify specific cognitive benefits from kangaroo care.

 

To maximize the impact and reliability of future studies, there are multiple challenges to consider. For instance, different developmental trajectories are associated with various gestational ages of the preterm population. To address this challenge, studies should either select a particular stage of prematurity or stratify results on the basis of birth gestational age. In addition, kangaroo care seldom occurs as an isolated intervention but rather is part of an individualized developmental program. Study designs must isolate the effect of kangaroo care from other developmental interventions. Therefore, it may be appropriate to compare neurodevelopmental outcomes in infants who receive the same developmental interventions but different doses of kangaroo care. Studies must also control for known factors that influence cognitive development, such as parental education, socioeconomic factors, breast-feeding, and high protein nutritional supplements, such as Prolacta. Another challenge is that there are multiple different mechanisms to explain why kangaroo care may improve neurological development. It is possible that one of the short-term benefits of kangaroo care is solely responsible for long-term differences in cognitive function or it is possible that multiple short-term benefits of kangaroo care have an additive or synergistic effect on neurodevelopment. Furthermore, kangaroo care may be neuroprotective or may actually promote synaptic growth and development. Studies should be designed to determine these mechanisms.

 

This research presents an ethical challenge as well. Given that short-term benefits are well documented, it may be unethical to prevent groups of infants from receiving kangaroo care. To address this challenge, it would be appropriate to examine the effect of different doses of kangaroo care.

 

CONCLUSION

Preterm birth affects 11.8% of the population and often leads to poor executive functioning and cognitive performance.1 As more infants born preterm are surviving, it is imperative to address deficits in neurodevelopmental outcomes. Although current research is limited in supporting kangaroo care as a strategy for improving neurodevelopmental outcomes, evidence suggests that kangaroo care has many short-term benefits that may positively influence the developmental sequelae, cognitive function, and school performance in children born preterm.

 

Such research has important implications for nursing practice. The discipline of nursing seeks to promote health and development through holistic care. Kangaroo care is an intervention that promotes the psychological, behavioral, and physiological well-being of not only the preterm infant but also the parents. Nurses can help mitigate the risk of the NICU environment by facilitating kangaroo care to promote the health and development of the preterm infant.

 

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cognitive function; kangaroo care; neurodevelopmental outcomes; preterm infant