Babies born at the lighter end of the normal weight range still go on to develop lower IQs, say US researchers.
Previous studies have found that babies born under 2.5 kilograms score lower on IQ tests as children 鈥� but this is the first to find a link between normal birthweights and IQ, says the team from the New York Academy of Medicine.
This shows that 鈥渂irthweight variation has implications for health and development even within the normal range at birth,鈥� says Thomas Matte, who led the research.
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The team looked at the birthweights and results of IQ tests taken at age seven of more than 3000 children in the US. They found that the link between size and IQ score held true even when the children鈥檚 mothers鈥� age, education and socioeconomic status were taken into account.
The reason for the finding is unclear, says Matte. 鈥淚t could be that the same factors that restrict fetal growth more generally may also impair optimal brain development 鈥� or that the hormonal factors that play a role in regulating fetal growth may also influence brain development,鈥� he told New 杏吧原创.
Big boy
Birthweight had much more influence on boy鈥檚 IQ scores than girls鈥�, Matte adds. A one kilogram increase in birthweight related to a 4.6 increase in IQ point score among boys, but only 2.8 points in girls.
鈥淥ne reason boys might be more susceptible to the effects of fetal growth restriction is that they grow more rapidly in the latter part of pregnancy and are larger at birth. The more rapidly growing boys might then be more sensitive to growth restriction,鈥� Matte says.
Sex differences in brain development, which may be regulated by hormones, might also explain the results, he says.
Maternal smoking, alcohol or drug use and multiple births are the main causes of smaller birthweights.
Programmes to help boost cognitive development in low birthweight children do exist. But boosting IQ is a different matter, says Matte. 鈥淎s far as I am aware, there is no evidence that additional help in school can boost IQ.鈥�
Journal reference: British Medical Journal (vol 323, p310)
