Nov. 11, 2002 -- Preterm infants tend to process information more slowly than those born on time, and the gap does not disappear with age, new research suggests. The findings may help explain an observed link between prematurity and lower IQs.
Researchers at New York's Albert Einstein College of Medicine compared the thinking skills of 153 full-term babies during the first year of life with those of 53 babies born prematurely. The babies were shown pictures of two faces at regular intervals, but one of the faces remained the same and the other was changed each time the pictures were shown. The trial continued until the infant showed a consistent preference for the new face.
"Much of our work builds on earlier discoveries regarding the predilection of infants to look at things they haven't seen before," lead researcher Susan A. Rose, PhD, tells WebMD. "Animals do this, too, and it is a good way to study memory."
The researchers found that the preterm infants -- all of whom weighed less than or 3.85 pounds at birth -- processed the paired faces more slowly than the full-term babies in a series of tests given until the age of 12 months. The preterm infants took about 20% more attempts and roughly 30% longer than their full-term peers to study the paired faces and reliably recognize the new faces. The findings are reported in the November issue of the journal Developmental Psychology.
Even as early as 5 months of age, preterm babies processed the paired faces much more slowly. The findings are similar to those seen in studies involving 11-year-old children born prematurely, also conducted by Rose and her colleagues.
"We have identified problems in speed of processing information in this older age group, and now we have identified a similar problem in infancy," Rose says. "This suggests that processing speed is something of a building block for cognition."
Preterm babies who experienced common health problems at birth related to lack of oxygen, such as respiratory distress syndrome, were more likely to show delays in processing information than premature babies who did not have the health problems.
It is known that lack of oxygen can damage a part of the brain responsible for forming, sorting, and storing memories, known as the hippocampus, and Rose says this may at least partially explain her group's findings.
Separate studies suggest that about one-third of prematurely born infants experience academic difficulties later in life. And a large study examining the lowest birth-weight babies, published earlier this year, found that they had IQs that averaged five points lower than their full-term peers.
Neonatologist Maureen Hack, MD, of Cleveland's Case Western Reserve University, says it is no surprise that premature infants tend to lag behind full-term children in intelligence tests, but she says this does not mean that every prematurely born child will have problems.
"We know that as a group premature babies are more likely to have developmental delays and lower IQs," she tells WebMD. "But there are a lot of factors involved here, including the length of gestation and how sick they were when they were born."