Cognition and Learning
Research has consistently demonstrated a greater risk for learning-related problems in preterm, low birth weight children as they progress through infancy, preschool, and elementary school.[15,24,25] However, little research has explored the long-term effects of prematurity and low birth weight on cognitive and academic outcomes into adolescence and adulthood.[26,27] Studies have demonstrated significantly poorer cognitive and academic outcomes in children born preterm and/or with low birth weights compared with children born full term.
Many preterm infants exhibit early cognitive and learning problems that present as expressive language delays, visual-motor and visual-spatial deficits, and/or attentional difficulties during the first few years of life.[17,18,28,29] These early deficits are believed to be associated with later academic and learning problems.[30,31,32] When premature, low birth weight children reach school age, they exhibit a higher rate of learning disabilities and lower scores on tests of reading, writing, math, spelling, and executive functioning.[33,34,35,36]
While most children born preterm with VLBW or ELBW score within normal limits (≥85) on IQ tests, these children score significantly lower and demonstrate higher rates of subaverage IQ (<85) than their full-term peers. Bhutta et al[24] conducted a meta-analysis of studies examining school-age children born preterm and found that preterm children exhibited significantly lower IQ scores than full-term controls. The weighted mean difference in IQ scores across the 15 studies was 10.9 points. Furthermore, Grunau et al[16] found that 9-year-old ELBW children's mean Full Scale, Verbal, and Performance IQ scores were 15 to 17 points lower than those of full term controls. Among the children with ELBW, 19% had either a Verbal or Performance IQ score in the below average range (<85) compared with 3% of the control group. Another study by Hack et al[26] looked at IQ scores at 20 years of age and found that VLBW young adults demonstrated a significantly lower mean IQ score than full-term controls (87 v 92; P < 0.001). Moreover, there was a higher frequency of below average IQ, with 49% of the VLBW group and only 33% of the control group scoring below 85.
It is interesting to note that the ELBW and full-term children in the Grunau et al study exhibited much lower rates of below average IQ (19% and 3%, respectively) than the VLBW and full-term children in the Hack et al study (49% and 33%, respectively). This considerable discrepancy between the overall rates of below average IQ scores could be because of the fact that the Hack et al cohort included children with neurosensory impairments such as blindness, hearing loss, and cerebral palsy, while the Grunau et al study excluded such children. Furthermore, differences in the socioeconomic status (SES) of the two study cohorts may have contributed to the substantial discrepancy in the rates of below average IQ. In particular, participants in the Grunau et al study were predominantly middle class, whereas Hack et al's poorer performing study group included more lower-income participants. Studies have shown that children living in socioeconomically disadvantaged homes tend to demonstrate lower average IQ and language scores than children from more advantaged backgrounds. For example, in a meta-analysis of over 100 research studies, the average correlation between SES indices and children's IQ scores was 0.40, and the average correlation between SES and verbal achievement was 0.31.[37]
Once again, it is important to note that while ELBW and VLBW preterm children and young adults do demonstrate significantly lower mean IQ scores than full-term controls, the majority of these low birth weight children and young adults (more than 50%) score within normal limits on IQ tests. It should also be noted that neonatal medical conditions such as intrauterine drug exposure,[3,38] perinatal brain injury,[10,22,39] and respiratory problems[21,40] have been found to be associated with deficits in IQ.
Many studies have found significant impairments in the language development of preterm, low birth weight children compared with children born full-term. In particular, research has indicated deficits in expressive language,[29,41] receptive language,[17,18] word retrieval and comprehension,[42] word production,[43,44] short-term auditory memory,[45] and speech articulation.[46] As many as 22% to 28% of premature, low birth weight children present with language deficits within the first few years of life, which is significantly higher than the general population.[47,48] However, as with IQ, the majority of preterm, low birth weight children do not demonstrate language delays.
Language impairments have also been found to be associated with other neonatal medical conditions such as perinatal brain injury,[45,49,50] asphyxiation,[50] respiratory disease,[51] and prenatal drug exposure.[52]
Premature, low birth weight children also demonstrate deficits in visual-motor and visual-spatial skills. Several studies have found that premature children perform significantly worse than full-term controls on the Beery Test of Visual Motor Integration, which requires children to copy line drawings.[17,18,34,53] Premature, low birth weight children also exhibit lower scores than full-term controls on tasks such as block design,[53,54] spatial relations,[55] shape rotation, and line slopes.[42] It has been suggested that these visual-motor and visual-spatial deficits may be the result of small brain lesions in the cerebellum, parietal cortex, or basal ganglia caused by medical conditions such as poor oxygen intake (ie, hypoxia, asphyxia, chronic lung disease), intraventricular hemorrhage, and seizures, as well as physiological stress in the extrauterine environment.[8,29]
In terms of the effects of other adverse neonatal conditions, van den Hout et al[53] found that 5-year-old children born preterm who presented with PVL exhibited a significantly higher frequency of impairments on visual-motor and visual-perceptual tasks compared with premature infants that were neurologically healthy as well as those that suffered IVH or HIE. Furthermore, Katz-Salamon et al[55] ascertained that preterm infants with chronic lung disease (CLD), but no IVH or PVL, performed more poorly than healthy infants on visual-spatial exercises (eg, block design) and visual-motor tasks (eg, activities requiring hand-eye coordination).
Another area of developmental disability in premature infants relates to sensory and regulatory issues. Preterm infants are able to take in information through each of the sensory systems including the visual, auditory, tactile, vestibular, and proprioceptive systems. However, they are not able to organize and regulate external and internal sensory input as well as a full term infant who is more neurologically mature and able to adapt to the world. In addition to demonstrating a higher incidence of basic sensory deficits such as hearing loss and blindness, preterm low birth weight infants also exhibit significantly more difficulties with self-regulation and organization of sensory input. They are more likely to present with oral defensiveness and feeding problems, tactile defensiveness, and general sensory integration problems, which is not surprising given that these infants spend the first few weeks or months of their life in an environment that is, by its very nature, more stressful and overstimulating than the intrauterine milieu. They spend the majority of their early days in a NICU bed, attached to monitors and bombarded with loud noises, bright lights, frequent handling, and invasive procedures, with tubes and needles being placed in their nose, mouth, hands, feet, stomach, and/or head.
The synactive theory of neurobehavioral development, pioneered by Heidelise Als, categorizes infant behavior and development into several interactive subsystems associated with sensory processing, organization, and regulation.[56,57] Als found that, compared with full-term infants, premature infants demonstrated significantly poorer scores on the Assessment of Preterm Infants' Behavior (APIB), a measure of behavioral organization, attention to sensory stimuli, and self-regulation.[58,59]
Other studies have supported these findings that preterm infants and young children demonstrate difficulties with self-regulation as well as integration and organization of sensory information. Case-Smith et al[60] found that premature infants exhibited more problems with sensory responsiveness, namely more tactile defensiveness and sensory seeking behaviors, than full-term infants. Other studies have found that preterm neonates demonstrate significantly poorer inhibition of responses to auditory and tactile stimuli compared with full-term neonates.[61,62] Furthermore, studies have indicated that premature infants and young children have difficulties with recognition and integration of sensory information. For example, studies of cross-modal transfer (recognition of a stimulus when presented independently across two different modalitiesie, oral and tactile) have found that children born preterm perform significantly worse on these sensory integration tasks.[63,64] This relates to previously discussed findings that premature, low birth weight children present with deficits in visual-motor and visual-spatial skills, which require integration of information across sensory modalities.
When considering premature versus full-term infants' abilities to regulate their behavioral and physiological responses to stimuli, studies have found that preterm neonates perform more poorly on measures of self-regulation, as well as state and autonomic regulation.[65,66,67,68] There is also evidence that prenatal exposure to drugs such as cocaine, negatively affects infants' capacity to regulate their behavior and arousal.[69,70,71] These early deficits in behavioral, state, arousal, and autonomic regulation, as well as problems with integration and organization of sensory information during infancy, are likely related to later deficits in children's attention regulation and executive functioning, which will be discussed in the following section.
Premature, low birth weight children demonstrate poorer attention and executive functioning skills in relation to full-term children.[24,72,73,74] Research has shown that deficits in attention are associated with problems in executive functioning.[74] Both attentional processes and executive functioning are regulated within the cerebral cortex, an area of the brain that is still developing in the premature infant. It is posited that preterm infants' early exposure to the nonuterine environment may have a negative impact on the neurological processes occurring in the brain, apart from the effects of specific adverse medical conditions. In particular, the organization, differentiation, and selective pruning of specific neurons may be disrupted, thus resulting in less organized, less efficient information processing.[8]
Many studies have found higher rates of attentional problems in premature, low birth weight children.[73,75] A recent meta-analysis found that 10 of the 15 studies reviewed demonstrated a significantly greater prevalence of attention problems in premature versus full-term children.[24] In a study by Sterqvist and Svenningsen,[76] 20% of 10-year-old very low birth weight, preterm children (compared with 8% of full-term children) were found to suffer from attention deficits. Similarly, Botting et al[77] found that 23% of very low birth weight children (v 6% of full-term peers) exhibited attention deficit disorders. It has been noted that premature, low birth weight children are more likely to have the type of attentional problems that are not associated with hyperactivity or conduct disorder, which are often seen in the general population.[78,79,80]
A study by Whitaker et al[81] found that parenchymal lesions and enlarged ventricles in premature, low birth weight neonates are significantly predictive of later attention deficit disorders. Children prenatally exposed to drugs have also demonstrated problems with attention as well as executive functioning.[70,82]
Attentional capacities are believed to be a fundamental component of higher order processes such as executive functioning. Executive functioning can be defined as the central processing, organization, and integration of separate pieces of information. It is posited that overall cognitive and learning deficits seen in premature, low birth weight children may be the result of a central deficit in simultaneous processing of multiple pieces of information across one or more sensory modalities.[78,83] As previously reported, Rose et al[64,84] found that preterm, low birth weight infants demonstrate poorer unimodal and cross-modal processing and integration of visual and tactile information, which is linked to later problems with cognition and learning. A study by Wall[74] found that 5- to 7-year-old children born preterm performed significantly worse than full-term controls on executive functioning tasks such as Visual Search, Verbal Fluency, and the Tower of Hanoi; the lower performance of these preterm children was associated with lower IQ scores as well as higher levels of attentional problemsnamely impulsivity and hyperactivity. It is likely that deficits in executive functioning and attention are related to the many learning disabilities that emerge in premature, low birth weight children once they reach school.[78]
Children born preterm with low birth weight are more likely to exhibit learning disabilities in math, reading, writing, and spelling than full-term children, even when looking only at those children who score within the normal range for IQ.[23,26,27,34] Learning disabilities in school-aged children have been found to be associated with earlier deficits in attention regulation and integration of sensory information.[16,23,78] Premature, low birth weight children tend to demonstrate more generalized learning problems rather than specific learning disabilities (ie, only a reading problem). This supports the theory that preterm children's learning problems are caused by a global processing deficit rather than difficulties with isolated skills.[78] Once children reach school, greater demands are placed on them with regard to logical reasoning and processing of higher-level visual, spatial, and verbal information. Several studies have also found an association between early processing of visual-motor and visual-spatial information, which requires cross-modal information processing, and later learning disabilities.[16,78,85]
NAINR. 2003;3(3) © 2003 W.B. Saunders
Cite this: Developmental Outcomes of Premature, Low Birth Weight, and Medically Fragile Infants - Medscape - Sep 01, 2003.
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