Cognitive abilities of low birth weight children show dramatic improvement

Our findings are good news for babies who are born low birth weight

The gap between the cognitive abilities of children born with a low birth weight and those born with a normal weight has decreased by 50 per cent over the last 40 years or more, according to new research from LSE and the Max Planck Institute for Demographic Research.

The paper, which appears in the journal Proceedings of the National Academy of Sciences (PNAS), found that while low birth weight children(1) continue to have worse cognitive scores than children born with a normal weight(2) when tested at ages 10 or 11(3), the disparities have declined dramatically.

Dr Alice Goisis, a researcher at LSE and one of the authors of the paper, said: “Our findings are good news for babies who are born low birth weight and are likely to reflect improving health care for mothers and babies over the last four decades.”

“In particular, neonatal intensive care units were introduced in the 1970s, along with other advances in medical technology and drugs. These developments have helped prevent brain damage and other negative consequences often associated with low birth weights. Indeed, many more of these babies are surviving, which makes our findings even more striking”.

This is the first study to analyse whether the association between low birth weight and cognitive development has changed over time, in light of advances in neonatology and obstetric practice.

Low cognitive ability can negatively impact an individual’s educational attainment, the type of job they end up doing, as well as the likelihood of long term illness in later life.

Dr Goisis said, “Despite the many medical advancements we have seen, there remains a disadvantage associated with low birth weight that may be due to both social and biological factors, and that appears to be difficult to overcome.”

The researchers analysed data from the 1958 National Child Development Study, the 1970 British Cohort Study and the 2000-2002 Millennium Cohort Study. They took account of family characteristics, sex and whether the child was a first born – however, these did not explain the striking differences between cohorts.

Across all the studies, and compared to normal weight children, low birth weight children were more likely to have come from more disadvantaged families, from families in which the mother had poor health behaviours during pregnancy and did not breastfeed. Low birth-weight children were more likely to have been a first born and a girl.

Notes for Editors

(1) Low birth weight babies are those born weighing less than 2.5kg/ 5lbs 5oz
(2) Babies born with a normal birth weight are defined as those born weighing between 2.5-4.5kg/5lbs 5oz -9lbs 9oz,
(3) Children’s cognitive development was measured using a verbal ability test, which is a good proxy for general cognitive ability scores.