NEW YORK - Adults who were born prematurely may have a higher risk of the seizure disorder epilepsy than those who were born full-term, a new study suggests.
The findings, from a study of 630,000 Swedish adults ages 25 to 37, add to evidence linking early delivery to the disorder.
Past studies have found a correlation between preterm birth and epilepsy in children and teenagers.
This latest report extends the link to adulthood.
Researchers found that of everyone in the study, all of whom were infants born in Sweden between 1973 and 1979, just 922 people -- or 0.15 per cent -- were hospitalized for an epileptic seizure at some point between 2005 and 2009.
That rate was nearly five times higher, however, at 0.7 per cent, among people who were born very early -- between the 23rd and 31st week of pregnancy.
Even those born moderately premature, during the 35th or 36th week, had a higher rate of hospitalization for epilepsy, at 0.25 per cent.
"The risk is still very low," said lead researcher Dr. Casey Crump, of Stanford University in California.
But, he told Reuters Health, it had been thought that the correlation between preterm birth and epilepsy might fade as people move into adulthood.
This study suggests that's not the case.
The findings, reported in the journal Neurology, do not prove that preterm birth, per se, causes epilepsy.
"This doesn't necessarily mean there's a direct effect," Crump said.
One possibility, he noted, is that certain pregnancy-related complications that lead to preterm birth explain the connection -- such as pre-eclampsia or infections that may, in some cases, lower the amount of oxygen getting to the fetal brain.
But it's also possible that early birth, itself, impairs normal brain development, Crump said.
Epilepsy is a neurological disorder that causes occasional disruptions in the brain's electrical activity; that leads to brief changes in a person's consciousness, body movements or sensations -- better known as an epileptic seizure.
In most cases, the exact cause of a person's epilepsy is unknown.
But it can sometimes be traced to a specific problem, like a head injury.
In the US, it's estimated that about 2 million people have epilepsy.
It is often diagnosed in childhood, but can arise at any age.
The current findings are based on data from a national Swedish birth registry.
Of 630,090 people in the registry born between 1973 and 1979, just under 28,000 were born preterm (before the 37th week of pregnancy).
Crump's team tracked how many people were discharged from the hospital with a diagnosis of epilepsy between 2005 and 2009.
That diagnosis was not necessarily the first time a person was diagnosed with epilepsy, though.
When the researchers considered all adults born prematurely, 0.3 per cent were hospitalized for epilepsy between 2005 and 2009. And 1.1 per cent had been hospitalized for the disorder at some point in their lives.
That compared with just over 0.1 per cent and about 0.7 per cent, respectively, of people born full-term.
Crump said that doctors, parents and adults who were born preterm should be aware of the relatively greater risk.
But, noting that even the highest risk group had an epilepsy rate of under one per cent, he also said that no one should be "alarmed" by the findings.
"This also highlights the need for better prevention of preterm birth," Crump added.
There are no guaranteed ways to prevent preterm labor.
But experts recommend that women try to lower their risk by not smoking, and making regular prenatal doctor visits to catch and control conditions like diabetes and high blood pressure, which can raise the odds of early delivery.