IQ Linked To Birth Weight,
Even In Healthy Babies
Excerpt By Suzanne Rostler, Reuters Health Writer

NEW YORK (Reuters Health) - Achievement-minded parents can enroll their toddler in early preschool or sign up their 6-month-old for music class but according to researchers, these attempts to raise a child's intelligence quotient (IQ) may be in vain.

Their preliminary study found that a child's weight at birth--even within the normal range--was directly related to IQ at the age of 7 years. As a group, low birth weight babies, or those weighing less than 5.5 pounds, are known to score lower on intelligence tests by the time they enter school. The relationship between birth size and IQ has been less clear among normal birth weight children, however.

``The main implications are that variation in fetal growth may be related to variations in brain development and that the mechanisms may differ from those that seem to explain some of the impact of low birth weight on neurodevelopment,'' Dr. Thomas D. Matte, the study's lead author, told Reuters Health.

For instance, very low birth weight babies, or those weighing 3.3 pounds or less, are more likely to have vascular problems that may influence the development of the brain.

``In normal birth weight babies, presumably some other mechanisms are at work,'' said Matte, an epidemiologist from the New York Academy of Medicine in New York City.

The investigators also found that the relationship between birth weight and later IQ was stronger for boys than for girls. For every 2.2-pound increase in birth weight, IQ scores rose by an average of 4.6 points among boys and 2.8 points among girls, the researchers report in the August 11th issue of the British Medical Journal.

However, Matte stressed that the findings need to be confirmed in other groups of children before scientists can know with certainty how a child's weight at birth, when considered in the healthy range, affects brain development and why it might be different for boys and girls.

``Any explanation is speculative at this point,'' Matte said in the interview.

The researchers used standard tests to measure intelligence in more than 3,400 children in 12 cities, at the age of 7 years. The group of children included siblings to help account for social and economic differences among families. None of the children were premature and most weighed more than 5.5 pounds at birth.

Head circumference at birth, which is used as a marker of brain growth, did not appear to explain the relationship between birth weight and childhood IQ. And among same-sex siblings, birth weight was significantly related to IQ only in boys.

In other findings, lower birth weight and lower IQ scores were more likely in children of younger mothers, those with lower educational levels, non-white women and low-income women.

SOURCE: British Medical Journal 2001;323:310-314.

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