Part one of the article provided and introduction (click here for part one) and part two discussed some medical issues with preterm babies (click here for part two). This final section discuses cognitive issues.
Cognitive and other Behavioral Sequelae
Deficits in Intelligence
Even though the majority of children even born at fewer than 26 weeks of gestation often have cognitive and IQ scores within the lower average ranges there are still some interesting trends in the research regarding the cognitive performance of preterm children.
This paper has already discussed the potential for preterm infants to qualify for a diagnosis of mental retardation; however, even preterm children that do not have major impairments demonstrated lower than expected IQ attainment. This is important because aspects of intelligence have been demonstrated to be a major factor associated with developmental delays in children (Marlow, Wolke, Bracewell, & Samara, 2005).
Sagial and Doyle (2008) report studies that indicate that infants born before 28 weeks of gestation when tested at eight years of age scored poorer than controls of normal birth weight on measures of full-scale IQ. The magnitude of the difference between the two groups was between a half and three quarters of a standard deviation suggesting that the difference in IQ reflected general abilities and not specific intellectual abilities.
Marlow, Wolke, Bracewell, & Samara (2005) compared IQ attainment of extremely preterm children born before 25 weeks of gestation to normal term children at six years if age. The mean difference in the scores for overall cognitive ability (IQ) between the extremely preterm group and the control group of classmates was 24 IQ points with a 95 percent confidence interval of 20 to 27 IQ points. This is an amazing large difference. In the control classmate group the IQ scores of the boys were not significantly different from the IQ scores of the girls; however, among the extremely preterm group the boys had a mean difference of 10 IQ points lower than the girls. In an ANOVA analysis the interaction between sex and group was highly significant (p = 0.002). The researchers decided that perhaps physical disabilities could confound the results, but the effects remained robust even after the exclusion from the analysis of children with physical disabilities (a mean difference of 20 IQ points and a 95 percent confidence interval of 17 to 23 IQ points. Although there also appeared to be a significant decrease in the IQ scores with decreasing gestational age from 25 to 23 weeks of gestation, this trend was found not to be significant after the researchers adjusted for gender.
Weisglas-Kuperus, Hille, Duivenvoorden, Finken et al. (2009) performed a very interesting study using data from the Collaborative Project on Preterm and Small for Gestational Age Infants in the Netherlands (POPS). The POPS is an ongoing study on the effects of prematurity on later outcomes in children. Five hundred and sixty two preterm young adults (mean age 19) completed the intelligence test used in the study. The mean IQ for the preterm groups were 96.4 for a gestation age of less than 32 weeks and 98.4 for a gestational age greater than 32 weeks with the overall mean IQ 97.4. Interestingly there were several variables that affected overall IQ scores. The relevant variables include the observation that a rise of one week in gestational age was associated with a rise in 1.3 IQ points. When compared with infants who were born at 36 weeks of gestation children born at 26 weeks of gestation displayed an average 13.0 lower IQ points. Another interesting finding was that in this group without major impairments the parental education of the child was the best predictor of the child’s later intelligence.
Other Problems Associated with Preterm Children Related to Developmental Delays
Johnson, Wolke, Hennessy, & Marlow, (2011) re-assessed part of the cohort previously described by Marlow, Wolke, Bracewell, & Samara (2005). Two hundred and nineteen of the original cohort was reassessed at 11 years of age along with 110 children of the original normal term comparison group and 43 new normal term comparison children. This marks an important development in the understanding of preterm infants as following a group of children into late elementary school age can offer very important insights into academic functioning, social adjustment, and other related issues for this special group of children.
Within the cohort of preterm children there was a group of children that had serious neuro-cognitive impairments and that group will not be included in this discussion of the findings as these children have been previously discussed in the sections on cerebral palsy and mental retardation. Of the 120 other preterm children a comparison of academic achievement scores indicated that the preterm children without serious cognitive impairments performed at a about a half to a full standard deviation below their full term peers on measures of word reading, reading comprehension, decoding of words, math reasoning, and numerical operations. However, the overall composite scores were lower than expectation for the preterm group indicating that this group experiences general difficulties with academic tasks.
The researchers then performed a linear stepwise regression analysis of neonatal variables and 30 month neurodevelopmental outcomes. Up to 43% of the variance in academic attainment was accounted for by the neonatal variables. The factors of male gender, lower gestational age, vaginal breech delivery, and indices of neonatal illness including abnormal cerebral ultrasound scan, necrotizing enterocolitis requiring surgery, and postnatal steroid use were associated with lower reading scores in the preterm group, whereas higher social economic status and being breast fed were associated with higher reading scores. Similar findings were observed for math scores with the addition of higher maternal education also predicting higher math scores.
Very preterm children have also been demonstrated to display higher rates of difficulties in other cognitive areas, such as attention, visual spatial processing, and executive functions (executive functions are processes that bring about purposeful behavior, such as abstract thought, sequencing and shifting between different concepts, understanding relationships, impulse control, etc. that are important in the child’s cognitive functioning, their daily behavior, social interactions and emotional control). Marlow Hennessy, Bracewell, and Wolke (2007) analyzed data taken from the original participants in the earlier Marlow, Wolke, Bracewell, & Samara (2005) study. Measures of assesses planning, monitoring, self-regulation, and problem solving and visual attention (executive functions) and visuo-spatial and sensory motor tasks. Children with severe cognitive disorders were excluded from the preterm group. These findings indicated that the preterm group performed significantly poorer on all measure compared to the full term group; however, most of the discrepancies were in the range of a standard deviation below the full term group indicating that the preterm group did not perform in the clinically impaired range, but performed lower than expectation. Other research comparing scores obtained on measures of executive differ by about a standard deviation for preterm children without severe deficits compared to full term children (Sagial & Doyle, 2008).
Other difficulties such as higher rates of ADHD, depression, and behavioral problems have also been observed preterm children and may persist later into adolescence and adulthood (Sagial & Doyle, 2008).
Conclusions
The literature on the effects of being born preterm indicates that most of the preterm children do not have severe deficits that result in serious developmental delays; however, this group is in a higher risk group as the prevalence of serious developmental problems such as mental retardation and cerebral palsy which occur at a much higher than the rate than these same disorders occur in the general population. There is a well demonstrated relationship between the time of gestation and the severity of the dysfunction in preterm infants. However, there appear to be some interesting alternatives being considered to cope with this problem such as treating preterm infants with thyroid hormones. This treatment could allow for more normal brain development to occur once the child is outside the protective and nutritive influence of the mother. However, most of the data regarding any such treatment is preliminary in nature, based on animal models, and it may be a while before actual treatments with human subjects will take place.
In preterm infants that do not have serious neurological or cognitive deficits the literature indicates that these children perform below expectation compared to children born at full term or compared to psychometric normative data on nearly all measures of cognitive ability and academic attainment. However, research indicates that it may not be correct to compare preterm children to other children without adjusting for age starting at conception. It also appears that these mild cognitive dysfunctions are moderated by environmental factors. Neonatal factors that contribute to neurobehavioral deficits would include the vulnerability of the infant’s immature brain both before and after birth, the many clinical problems that are specific to premature birth, any stressful environmental conditions occurring after or before birth, and of course drastic hospital procedures. In addition, lengthy neonatal hospital stays often experienced by preterm infants could conceivably hinder the quality of early and crucial infant-parent interactions. In these preterm children with and without major neurological impairment an optimal environment may be able to compensate for a cognitive or physical delay. Education and assistance to families of preterm children would also be helpful in assuring that these children will develop at a normal rate.
References
Beck, S., Wojdyla, D., Say, L., Betran, A.P., Merialdi, M., Requejo, J.H., Rubens, C., Menon,
R., & Van Look, P.F. (2010). The worldwide incidence of preterm birth: a systematic review of maternal mortality and morbidity. Bulletin of the World Health Organization, 88, 31–38.
Berbel, P., Navarro, D., Auso, E., Varea, E., Rodriguez, A.E., Ballesta, J.J., Salinas,
M., Flores, E., Faura, C.C., & Morreale de Escobar, G. (2010). Role of late maternal thyroid hormones in cerebral cortex development: an experimental model for human prematurity. Cerebral Cortex 20(6), 1462–1475.
Filippi, C.G., Ulug, A.M., Deck, M.D.F., Zimmerman, R.D., & Heier, L.A. (2002).
Developmental delay in children: Assessment with proton MR spectroscopy. American Journal of Neuroradiology, 23, 882–888.
Johnson, S., Wolke, D., Hennessy, E. M. & Marlow, N. (2011) Educational outcomes in
extremely preterm children: Neuropsychological correlates and predictors of attainment. Developmental Neuropsychology, 36 (1), 74 - 95.
Marlow N., Hennessy, E.M., Bracewell, M.A., Wolke, D. (2007). Motor and executive
function at 6 years of age after extremely preterm birth. Pediatrics, 120, 793–804.
Marlow, N., Wolke, D., Bracewell, M.A, & Samara, M. (2005). Neurologic and developmental
disability at six years of age after extremely preterm birth. New England Journal of Medicine, 352, 9–19.
Neubauer, A-P., Voss, W., & Kattner, E. (2008). Outcome of extremely low birth weight
survivors at school age: The influence of perinatal parameters on neurodevelopment. European Journal of Pediatrics, 167, 87–95.
Restiffe, A.P. & Gherpelli, J.L.D. (2006). Comparison of chronological and corrected
ages in the gross motor assessment of low-risk preterm infants during the first year of life. Arquivos de Neuro-Psiquiatria, 64 (2B), 418–425.
Saigal, S, &, Doyle, L.W. (2008). An overview of mortality and sequelae of preterm birth from
infancy to adulthood. Lancet, 371, 261–269.
Weisglas-Kuperus, N., Hille, E.E., Duivenvoorden, H.H., Finken M. J. J., Wit, J.M., van Buuren,
S., Goudoever, J.B., & Verloove-Vanhorick, P.S. (2009). Intelligence of very preterm or very low birth weight infants in young adulthood. Achieves of Disease in Childhood: Fetal Neonatal Edition, 94(3), F196– F200.
Rudy Hatfield - I am a clinical neuropsychologist with extensive experience in the assessment and treatment of neurological and psychiatric disorders. I ...
Join the Conversation