Many studies have shown that low birthweight babies have lower IQ test scores at school age.
Researchers at Columbia University, and the New York Academy of Medicine examined the relation between birthweight and measured intelligence at age 7 years in over 3000 children. Most of the children had a birthweight in the normal range (2500 grams and above).
They found that, on average, IQ at age 7 years was directly related to birthweight among these children. This was so 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 birthweight 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.
|Association between birthweight and IQ stronger in boys.
|British Medical Journal|
IQ was associated with differences in birthweight 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.