News | December 19, 2016

Cognitive abilities of low birth weight children show strong improvement

A low birth weight is considered a risk factor for decreased cognitive abilities in later life. This risk factor now seems to be dissolving; it is much less pronounced in younger birth cohorts.

Children born with a low birth weight have on average more health problems and poorer cognitive abilities than children of normal birth weight, as numerous studies have shown. However, medical care for babies of low birth weight has improved remarkably over the last decades. As a result, the disadvantage suffered by low birth weight babies may be changing.

MPIDR-director Mikko Myrskylä, together with colleagues from the London School of Economics, has now investigated how these improved external conditions affect the cognitive abilities of children with low birth weight. Their results, published in the current issue of the Proceedings of the National Academy of Sciences (PNAS), show that the relationship between low birth weight and reduced cognitive abilities in childhood has been declining by two thirds since the 1950s.

For their study, the scientists used data from three British cohort studies. In these surveys, which began in 1958, 1970, and 2000/2002 respectively, the development of around 10,000 children in each study was recorded in terms of education, income, and health over a period of several decades.

The researchers divided the children of each cohort into two birth weight categories, namely those with a low birth weight of less than 2500 grams and those born with a normal birth weight (2500 to 4500 grams). As a measure of cognitive abilities, they used the results of verbal tests undergone by the children when they reached age 10 or 11 and which are known to be good indicators for the intelligence quotient.

The researchers found that in all three cohorts examined, the children with a low birth weight on average performed worse in the verbal tests than those of normal birth weight. However, the difference in the younger cohort (2000/2002) was two thirds smaller than in the first two cohorts (1958 and 1970).

"Especially since the 1970s, medical care of newborn babies has improved a lot," explains Myrskylä. In the seventies, neonatal intensive care medicine was introduced. Since then, small or premature babies have been monitored around the clock, and they have been ventilated. There are also new drugs that support premature babies in their development. "These advances in medicine have probably led to the prevention of many brain damages that before had been common for babies of low birth weight," says Myrskylä. These results are supported by findings for the 2000/2002 cohort: The proportion of very small babies, namely those weighing less than 1500 grams at birth, increased across the cohorts. In the younger cohort, even children who started life under very difficult conditions and who had little survival chances a few decades ago gave better results in cognitive tests.

The researchers also found that across the cohorts, one group of children performed consistently below average, namely children from socially disadvantaged families. "The associations between a disadvantaged family background and cognitive development are clearly stronger than those with low birth weight. It is wonderful that the disadvantage suffered by low birth weight babies is declining; it would be even better if we saw the same for children coming from socially disadvantaged backgrounds," says Myrskylä.

More Information

Original Article: Goisis, Alice, Özcan, Berkay and Myrskylä, Mikko, Decline in the negative association between low birth weight and cognitive ability. Proceedings of the National Academy of Sciences of the United States of America (PNAS), 2016, ISSN 0027-8424