More than 10% of all babies are born preterm every year, and prematurity is a well-established risk factor for cognitive impairment at some level.

Prematurity affects working memory in particular

In a recent German study involving 1326 8-year-old children, it was found that being born preterm specifically affected the ability to solve tasks with a high cognitive load (i.e. greater demands on working memory), whereas tasks with a low load were largely unaffected.

These findings are consistent with other research suggesting that prematurity is associated in particular with difficulties in math, in complex problem-solving, and in simultaneous processing (such as occurs in recognition of spatial patterns).

There was also a clear dividing line, with deficits disproportionally higher for children born before the 34th week of pregnancy compared with children born after week 33.

Rate of cognitive impairment in premature infants

A Swedish study of 491 toddlers (2 ½ years) who had been born extremely preterm (less than 27 gestational weeks) found that 42% of them had no disability (compared with 78% of controls), 31% had mild disability, 16% had moderate disability, and 11% had severe disability. Unsurprisingly, there was an increase in moderate or severe disabilities with greater prematurity. There was no gender difference.

Cognitive impairment in premies linked to smaller brain tissue in specific regions

Why are some individuals affected by prematurity, why others aren’t? An analysis of brain imaging data of 97 adolescents who had very low birth weights, and whose academic progress has been followed, found that more than half of the babies that weighed less than 1.66 pounds and more than 30% of those less than 3.31 pounds at birth later had academic deficits. Academic deficits were linked to smaller brain volumes, and in particular to reduced volume of the caudate and corpus callosum, which are involved in connectivity, executive attention and motor control.

J. Jäkel, N. Baumann, D. Wolke (2013): Effects of gestational age at birth on cognitive performance: a function of cognitive workload demands, PLOS ONE,

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(2013).  Relation of neural structure to persistently low academic achievement: A longitudinal study of children with differing birth weights.
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Older news items (pre-2010) brought over from the old website

Intake of certain fatty acid appears to improve neurodevelopment for preterm girls, but not boys

A large randomized trial of infants born at less than 33 weeks' gestation from five Australian hospitals has found that girls who received a high supplementary daily dose of DHA (an omega-3 fatty acid) in either their breast milk or infant formula until their expected delivery date performed significantly better on a mental development test when they were 18 months old than girls who received a low dose. However, bafflingly, boys showed no effect.

Makrides, M. et al. 2009. Neurodevelopmental Outcomes of Preterm Infants Fed High-Dose Docosahexaenoic Acid: A Randomized Controlled Trial. JAMA, 301(2), 175-182.

Early cognitive tests of premature predict later development

A number of studies have shown that premature birth increases a child's risk of learning and other cognitive disabilities, including lower IQ, language delay, poorer school achievement and learning disabilities. A new study has now found that early cognitive deficits apparent at 7 months (such as poorer attention, slower processing speed and poorer recognition memory) fully account for lower cognitive scores of 2- and 3-year-olds. This suggests that cognitive difficulties can be identified early, with the hope of successful intervention.

Rose, S.A., Feldman, J.F., Jankowski, J.J. & Van Rossem, R. 2005. Pathways From Prematurity and Infant Abilities to Later Cognition. Child Development, 76 (6), 1172

Why premature brains improve over time

A new study explains why premature babies often develop better than expected. A mouse study has found that infants born prematurely and with hypoxia (inadequate oxygen to the blood) are able to recover some cells, volume and weight in the brain after oxygen supply is restored, by a process of neurogenesis.

Fagel, D.M., Ganat, Y., Silbereis, J., Ebbitt, T., Stewart, W., Zhang, H., Ment, L.R. & Vaccarino, F.M. 2005. Cortical neurogenesis enhanced by chronic perinatal hypoxia. Experimental Neurology, In Press.

Interestingly, another recent study, following up an earlier study when premature infants with respiratory distress syndrome were given inhaled nitric oxide (decreasing the risk of death or chronic lung disease), has found that the treatment also improve neurodevelopmental outcomes. 24% of those given nitric oxide had abnormal neurodevelopmental outcomes at two years of age compared to 46% in the placebo group.

Mestan, K.K.L., Marks, J.D., Hecox, K., Huo, D. & Schreiber, M.D. 2005. Neurodevelopmental Outcomes of Premature Infants Treated with Inhaled Nitric Oxide. NEJM, 353 (1), 23-32.

Effect of prematurity on brain worse for boys

A comparison of the brain volumes of 65 8-year-olds born prematurely to 31 children born full-term has found significantly smaller areas in the cerebral cortex, especially in parts responsible for reading, language, emotion and behavior. However, significant gender differences were found. Only the preterm boys showed significant reductions in white matter volume. Only the preterm girls showed a positive correlation between gray matter volume and cognitive outcome. The study suggests that the gender of the preterm child affects the way in which the developing brain is affected, and also suggests that boys are more negatively affected by prematurity. Previous studies have indicated more adverse cognitive outcomes for preterm boys than preterm girls. This latest study suggests that an approach to stimulate white matter growth in preterm boys would be promising.

Reiss, A.L., Kesler, S.R., Vohr, B., Duncan, C.C., Katz, K.H., Pajot, S., Schneider, K.C., Makuch, R.W., Ment, L.R. 2004. Sex differences in cerebral volumes of 8-year-olds born preterm. The Journal of Pediatrics, 145 (2), 242-9.

More evidence of long-lasting cognitive deficits in pre-term babies

298 children born during 1991-1992 with birth weights less than 1000g or born earlier than 28 weeks'gestation were compared with 262 randomly selected children with birthweights of more than 2499 g.The premature children scored significantly below the control group onIQ (an average drop of 9.4 points) and indices of verbalcomprehension, perceptual organization, freedomfrom distractibility, and processing speed. They also performed significantly worseon tests of reading, spelling,and arithmetic. Attentional difficulties, internalizing behavior problems, and immature adaptive skills were also more prevalent in the group.

Anderson, P., Doyle, L.W. & the Victorian Infant Collaborative Study Group. 2003. Neurobehavioral Outcomes of School-age Children Born Extremely Low Birth Weight or Very Preterm in the 1990s. JAMA, 289,3264-3272.

Low birth weight still impacting exam scores 16 years on

A study of 334 16-year-olds found that those who weighed 1,500 grams or less at birth, scored an average of 32.33 on their GCSEs (the researchers gave a numerical score to each GCSE grade, starting with eight for A*), compared to an average score of 36.78 for those with a normal birth weight. The difference was greatest for maths and statistics. There was no difference in results for geography and history, and the normal birth weight group achieved better results in general science and English. The participants were closely matched for school and several social variables.

Pharoah, P.O.D., Stevenson, C.J. & West, C.R. 2003. General Certificate of Secondary Education performance in very low birthweight infants. Archives of Disease in Childhood, 88, 295-298.

Cognitive abilities increase with time in most premature children

Many studies have found that children born prematurely with very low birthweight have an increased risk of many neurological problems, including cognitive handicaps. New research shows that most of these children improve significantly on tests of cognitive function during early childhood and score within the normal range on tests of verbal comprehension and intelligence by age 8.

Ment, L.R., Vohr, B., Allan, W., Katz, K.H., Schneider, K.C., Westerveld, M., Duncan, C.C., Makuch, R.W. 2003. Change in Cognitive Function Over Time in Very Low-Birth-Weight Infants. Journal of the American Medical Association, 289 (6), 705-711.

Pre-term infants' slowness in processing information still evident at 12 months

Pre-term infants tend to be slower at processing information than babies born full term. New research shows this deficit in processing speed (which can be shown, for example, in slower learning of new faces) is present at five months, and still evident at twelve months. Previous research has also indicated that a number of the medical risks suffered by pre-terms (such as respiratory distress syndrome)have an effect on processing speed. A deficit in processing speed has implications for measures of intelligence, language and academic achievement, such as reading, arithmetic and spelling.

Rose, S.A., Feldman, J.F. & Jankowski, J.J. 2002. Processing Speed in the 1st Year of Life: A Longitudinal Study of Preterm and Full-Term Infants. Developmental Psychology, 38 (6), 895–902.

Calculation difficulties in children of very low birthweight

Learning difficulties, including problems with numeracy, are common in Western populations. Many children with learning difficulty are survivors of preterm birth. Although some of these children have neurological disabilities, many are neurologically normal. A neuroimaging study of neurologically normal adolescent children who had been born preterm at 30 weeks gestation or less found an area in the left parietal lobe where children without a deficit in calculation ability have more grey matter than those who do have this deficit.

Isaacs, E.B., Edmonds, C.J., Lucas, A. & Gadian, D.G. (2001). Calculation difficulties in children of very low birthweight: A neural correlate. Brain, 124 (9, 1701-1707.