IQ linked to birth weight even among children of normal birth weight

August 09, 2001

Many studies have shown that low birthweight babies have lower IQ test scores at school age, but a study in this week's BMJ finds that the association between birthweight and childhood IQ also applies to children in the normal range of birth weight.

Researchers at Columbia University, and the New York Academy of Medicine examined the relation between birth weight and measured intelligence at age 7 years in over 3000 children, most of whom had birthweight in the normal range (2500 grams and above).

They found that, on average, IQ at age 7 years was directly related to birth weight among these children, even after factors such as mother's age, race, education and socioeconomic status were taken into account.

The association was stronger in boys than girls. For example, a 1000g increase in birth weight related to a 4.6 increase in IQ among boys but only 2.8 points in girls. Unlike most previous studies of this relationship, the authors also assessed this association within sibling pairs, eliminating the possible effect of social and economic differences between families. IQ was associated with differences in birth weight between boy sibling pairs but not girls.

These findings may have important implications for future research on the connections between fetal growth and brain development, conclude the authors.
-end-
Influence of variation in birth weight within normal range and within sibships on IQ at age 7 years: cohort study BMJ Volume 323, pp 310-314

BMJ

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