Serious health problems are significantly more likely to affect babies born just a few weeks prematurely than those born at full-term, according to new research.

The U.S. study found that late pre-term babies — those born between 34 and 36 weeks of pregnancy — are three times as likely to be diagnosed with cerebral palsy as full-term babies (born between 37 and 41 weeks of pregnancy).

The study, which will be published in the Journal of Pediatrics, also found that late pre-term babies were 25 per cent more likely than full-term babies of having learning, speech and other developmental delays or mental retardation.

While the overall incidence of cerebral palsy for full-term babies stands at two per cent, the study found that the number jumped to 7.3 per cent among late pre-term infants.

The study notes the findings are significant since earlier studies have only examined the link between very or moderately premature babies and cerebral palsy. Late pre-term births — which account for 70 per cent of all premature births in the United States — have not been heavily researched, says the study.

"The negative outcomes of many babies born late pre-term can no longer be described as temporary or benign," Joann Petrini, lead researcher in the study, said in a news release.

In an interview with the Canadian Press, Petrini noted that late pre-term babies are often treated as though they're full-term babies.

"I mean, they look chubby many times. They look healthy and many times are not and are discharged and may not get the attention that a pre-term baby needs," said Petrini, an expert in prematurity and director of the perinatal data centre at the U.S. national office of the March of Dimes, a charity devoted to preventing birth defects and infant mortality.

Results could be conservative

The study examined the neurological development of 140,000 babies born between 2000 and 2004 in Northern California. The babies in the study had gestation periods that started at 30 weeks and ranged higher.

The babies were born to parents who had health-care coverage through the Kaiser Permanente medical care program. The fact that the parents were affluent enough to have this health insurance coverage suggests the results may be conservative, Petrini said.

In Canada, 7.5 per cent of babies are born prematurely. Over 50,000 Canadians have cerebral palsy, according to the Ontario Federation for Cerebral Palsy.

Cerebral palsy is a neurological condition that affects motor abilities. The majority of those with the condition are born with it, and it can go months or even years without being detected.

The condition hampers co-ordination of body movements, and symptoms — such as stiffness, crouched gait or tremors — can range from mild to severe. There is no known cure, but it is not life-threatening.

With files from the Canadian Press