By the age of 16, children born very prematurely are able to catch up to kids born at full term in their ability to identify the names of things, according to a new study.
The results are a bit of good news among myriad reports detailing deficits in learning and cognition that are common among children born weeks or months before their due date.
"This leaves one on a high note, that some of these kids do well," said Dr H. Gerry Taylor, a professor of paediatrics at Case Western Reserve University, who was not involved in the study.
The Canadian and US researchers compared more than 300 children born early and weighing less than 1.5 kg to 41 children who were born after a full-length pregnancy of 37 weeks.
At ages eight, 12 and 16 years, the kids took several tests to measure their IQ and language skills. At each age, the premature children had IQs 15 to 17 points lower than their full-term counterparts.
On tests of word knowledge and spatial reasoning, both groups of children improved in their skills over time, but the scores of the kids born early continued to lag by similar margins.
However, one examination - called receptive vocabulary, in which kids are shown pictures of objects and asked to identify the correct picture for a given word - revealed a different pattern.
At eight years old, the premature kids scored 14 points lower on the vocabulary test than the other group. But every four years, these children closed the gap by four points, nearly catching up with the full term kids by the time they turned 16.
What causes this?
Taylor said that the reason premature children perform better on some tests and worse on others is likely because the risk for brain damage when babies are born early is higher for some parts of the brain and lower for others. "Some areas of the brain sustain more insult than others," he said.
A previous study on this same group of premature children reported that their language and intellectual skills suffered through the school-age years, compared to full term children.
The findings of this latest research "were encouraging, because we always focus on the negative" aspects of being born prematurely, said lead author Dr Thuy Mai Luu, a pediatrician and clinical researcher at Sainte-Justine University Health Center in Montreal.
Luu added that her results show that a subset of preemies performs normally on some language and problem-solving tests.
For instance, in a word comprehension test, 17% of premature children outperformed the full term group at eight, 12 and 16 years of age. An additional 38%of premature kids caught up to the full term kids by the age of 16.
On a visual problem-solving test, nearly half of the pre-term children performed just as well as the full term kids at each age.
Luu's group found that the best-performing kids who were born premature tended to have mothers with higher levels of education and to come from families with a higher socioeconomic status.
"We don't know the mechanism," Luu said. "That's the next step: to understand why they're doing better."
One possibility is that some children are better able to repair any brain damage done as a newborn, or perhaps they had less injury to begin with.
Another recent study found that children who have a delay in their speech – kids who have a limited vocabulary at two years of age - also catch up by the time they're five, with no impacts on their behavioural health.
Taylor said the results of this study, published in the Journal Pediatrics, are rare in that most other studies have reported that once deficits are established in pre-term children, they tend to remain.
"It's amazing that even with these areas of difficulty the children are able to compensate quite well, make use of their strengths, and go on to achieve," Taylor said.
(Reuters Health, Kerry Grens, July 2011)