PREMATURE babies have a higher risk of dying early as a young child or adult, a new study has shown.
Scientists looked at data on 600,000 people born in Sweden between 1973 and 1979.
Children were more likely to die in their first five years the earlier they were born.
The pattern faded away in late childhood and adolescence, but returned between the ages of 18 and 36.
During this age period, individuals were more likely to die if they were born pre-term.
In young adulthood, death rates per 1,000 "person years" ranged from 0.95 for those born most prematurely to 0.46 for those born after a full-term pregnancy.
The findings were published today in the Journal of the American Medical Association.
The researchers, led by Dr Casey Crump, from Stanford University in California, wrote: "The underlying mechanisms are still largely unknown but may involve a complex interplay of foetal and post-natal (post birth) nutritional abnormalities, other intra-uterine exposures including glucocorticoid (a steroid hormone) and sex hormone alterations, and common genetic factors."
They added: "Clinicians will increasingly encounter the sequelae (consequences) of pre-term birth throughout the life course and will need to be aware of the long-term effects on the survivors, their families and society."
Dr Crump, though, said the results, based on Swedish data, should not cause undue alarm.
"The absolute mortality was still less than one per 1,000 people per year, so it's very low."
Among young adults born at 22 to 27 weeks' gestation, the death rate was 0.94 per 1,000 people per year. For those born between weeks 37 and 42, considered full-term, the rate was 0.46 per 1,000.
Between 12 and 13pc of babies in the US are premature.