Link Probed Between IQ, Infant Head Size : Study Identifies Brain Growth Rate as Warning of Later Developmental Problems for Preemies

Subnormal head growth during just the first six to eight months of small premature babies’ lives may warn of irreversibly reduced intellectual ability, a new research study concludes.

And while several experts agree that small head size in tiny preemies is only a risk factor--not a guarantee of diminished intelligence--the finding underscores yet another complication brought on by advances in medicine: Survival rates for the tiniest of newborns--those weighing between 15 ounces and 2.9 pounds when they are born--represent both one of the greatest technological triumphs of medicine in the last 15 years and one of its most major quandaries.

A Critical Period

Moreover, what has become ever clearer is that the first year of life for such tiny newborns represents a profoundly critical period in their development.

The early months are especially crucial to tiny premature infants because they must catch up in many ways to normal-weight infants or remain significantly at risk for permanent handicaps, including paralysis, blindness and retardation.

In many of the nation’s most advanced neonatal intensive care units--high-tech centers that care for the smallest premature babies--three-quarters of babies in the smallest categories now survive. But what remains unknown is how well they will develop, intellectually and physically, in adult life. Most will probably develop normally, but many may face permanent handicaps.

Because the most advanced neonatal units have existed only since about 1975, no baby treated in the new system has yet attained adolescence, much less adulthood.

As many as 10% or 11% of all babies fall into the lightweight premature category. The precise organic causes of such extreme low birth weight remain unidentified.

But in a new research study published in this month’s issue of the journal Pediatrics, researchers have added new evidence to earlier findings suggesting that a child’s head growth and brain development in the first six to eight months of life may be a significant predictor of the child’s intelligence quotient at age 3 and beyond.

The new study was conducted by doctors at the Case Western Reserve University School of Medicine in Cleveland. The research was an extension of an earlier project in which, in 1982, the same team found small premature babies who did poorly during the first eight months of their lives exhibited the first signs, even at that age, of an early inability to develop normally.

The new Cleveland report also substantially agrees with a 1983 project at Duke University Medical Center in North Carolina that found the circumference of a premature baby’s head at 6 months--and perhaps even just 6 weeks--may signal an early warning of possible later intelligence deficits.

Both the Cleveland and Duke reports, their authors agreed, underscore the potential importance of such things as nutrition, intellectual stimuli and parent-child interaction in the first months of life.

Study Findings

At Case Western Reserve, a team headed by Dr. Maureen Hack followed 139 babies born in 1977 and 1978 and who weighed 2.9 pounds or less when they were delivered. After taking note of the children’s head circumferences starting when they were 8 months old, the team tracked the babies until they were 3, at which point IQ tests were administered.

The study found that, at 8 months, 14% of the children had head circumferences that were below normal and at age 3, 7% of the 139 babies were retarded and 25% were of borderline intelligence.

Both Hack and Dr. Steven Gross, of Crouse-Irving Memorial Hospital in Syracuse, N.Y., emphasized that a healthy majority of the babies--68% in the Cleveland study--were of at least normal intelligence when they turned 3. Gross headed the Duke study group in North Carolina in 1983.

Thus, to both Hack and Gross, small head size alone does not appear to unavoidably doom a tiny baby to a lifetime of substandard intelligence, but a tiny infant with a very small head at age 6 or 8 months has an apparently significantly increased risk of later developmental intelligence problems.

Both of the researchers discussed their findings in telephone interviews. They agreed that what remains unknown is how head-size growth can be promoted during the crucial early period and whether, as they grow older, children who were among the smallest of premature babies and had low IQs when they were 3 can narrow the intelligence gap.

Additional Research

Hack said she is currently working on a study to examine essentially the same group of babies and some born in 1979 when they turn 8, but the work--because the children involved won’t all have reached that age until late 1987--may not be ready for publication for as long as four years.

Gross said he is now doing additional research to try to identify factors in the first six or eight months of life that may influence head size and brain growth. A major problem, researchers agreed, is that many of these tiny premature babies are difficult to feed since they are often too sick to tolerate breast milk or formula and must be fed via plastic tubes inserted into their stomachs.

At birth, a normal baby’s head is about 13 inches around and, by age 1, the circumference usually increases to about 18 inches.

“In general, by age 2 or 3, there is a very good correlation between severe delay (in head growth) and longer-term outcome,” Gross said. “It is less clear for babies the closer you get toward the average size.”

“What influences head growth? That’s a difficult question. This group as all very small preemies who were very sick in the nursery and, for that reason, didn’t grow,” Hack said.

“Then when they went home, (did) the head growth catch up? Is the child going to compensate? It is subtle. In North America, you don’t have much severe malnutrition. In this country, it may be more a factor of the maternal-child interaction. The way the parents care for the child. We couldn’t get that out of our data because we don’t have measures for that sort of thing.”

In the newly published study, however, Hack and her team emphasized that head size is only one major predictor of subsequent intellectual development. Also critical are race and social class, with premature babies born to poor black mothers having by far the most significant risk of later intellectual deficit.