Young adults who were born very prematurely, but without any serious brain impairments, may still not be as mentally sharp as their peers, a small study published Monday suggests.
Finnish researchers found that of 208 young adults they tested, the half born at a very low weight – less than 3.3 pounds – generally had lower scores on some measures of memory, attention and other mental skills.
They also had a lower average IQ score, though it was still in the normal range, the researchers report in the journal Neurology.
"While we know babies born severely preterm generally achieve lower cognitive test scores, this is one of the first studies to look at how severely low birth weight impacts executive functioning, such as attention and visual memory, when these babies become young adults," senior researcher Katri Raikkonen, of the University of Helsinki in Finland, said in a news release from the journal.
The real-life impact of the lower test scores is not clear.
Test performance for the low birthweight group was lower, but still "normal," according to Raikkonen.
And, she noted in an email, the differences between the two groups are averages. That is, some preemies "fare better, others worse, which of course is the case for (full-term) babies as well," Raikkonen told Reuters Health.
"Our study shows group differences, and one cannot make individual-level conclusions from these findings," she said.
As far as school achievement, the preemie group was more likely to need remedial education. But academically, they ended up doing as well as their peers born full-term.
It's not clear how to interpret that, Raikkonen said. One possibility, she noted, is that remedial help in school is especially helpful for preemies, but that's not certain.
The findings are based on 103 adults in their 20s who were born weighing less than 3.3 pounds, and 105 born full-term. All took standard tests of memory, attention, planning and other cognitive skills.
On average, the low-birthweight group had a lower IQ – 102, versus just under 111 in the full-term group. But that score is still in the normal IQ range.
The low-birthweight group also tended to score a few points lower on the cognitive tests, though not on all of them.
When it came to school, many more low-birthweight adults said they had needed remedial help: 46 percent, versus 19 percent.
On the other hand, they ended up doing as well as the comparison group, with a similar grade point average and education level (an average of just over 13 years of schooling).
In the U.S., it's been estimated that about 12 percent of infants are born preterm. And survival rates for tiny preemies, like those in the current study, have risen substantially in the past few decades.
Still, those infants are at higher-than-normal risk of health problems in the long run. Another recent study also found mild learning problems in extreme preemies once they reached kindergarten.
The current work excluded preemies with any major neurological impairments, Raikkonen said. But it's still possible that more-subtle problems in early brain development could explain the lower test scores, she explained.
"Even in apparently healthy infants," she said, "minor brain insults may restrict later brain plasticity and brain maturation and manifest in altered neurocognitive functioning even in young adulthood."
"Plasticity" refers to the brain's ability to change in response to input from the environment, which includes recovering from injury. It's possible, Raikkonen said, that plasticity does not fully compensate for early brain injury in some preemies.
For parents of preemies, Raikkonen pointed out that "'normal' sensitive parenting, and stimulating environment, benefits development of all babies, regardless of their birthweight and length of gestation (pregnancy)."
She added that some evidence suggests that breastfeeding aids infants' development, particularly preemies' though study findings have not been consistent on that.