But researchers say they now have some reassuring news to report: Although those who start life as "extreme preemies" do face more health, social and economic difficulties during childhood or young adulthood, most of them are satisfied with their lives as adults.
"This self-assessment might be the most important fact overall," said study author Dr Brian Darlow, a professor of paediatric research at the University of Otago, Christchurch, in New Zealand.
More health problems
Darlow and his team have been keeping tabs on 230 young adults who were born at very low birth weights, around 13 kg or less. The young adults, who were born in 1986, sat down with researchers to answer questions about their lives, social circumstances and health.
The researchers also asked the same questions of 69 people who were the same age, but were born at normal weights.
Their findings are published in the journal Paediatrics.
As a group, the preemies hadn't gone as far in school as their normal-weight peers. They were about half as likely to have received a college degree. They also were more likely to say they didn't have friends or significant others, or to be sexually active. And they reported having more health problems and hospitalisations.
But the study authors said many of those statistical differences were driven by the 10% of very low birth weight babies who had more severe mental and physical disabilities at ages 7 and 8. By and large, the kids who were doing well in grade school continued to function well as adults.
There were no differences in rates of drug use, criminal activity, or mental or behavioural problems. Those who were small at birth were significantly less likely to report using illegal drugs.
Fully functioning adults
Perhaps most important of all, they scored the same on measures of self-esteem and life satisfaction as those who were normal weight at birth.
Darlow said the study participants, who are now aged 26 and 27, are undergoing another battery of psychological testing and will soon repeat the same questionnaire. It's his belief that they probably won't see any difference in measures of friendships or social functioning this time around.
"My guess is that the social isolation will be much less and probably no longer present at all, so in that area maybe they have just taken a little longer to catch up," he said.
Another expert said the findings should comfort parents of very low birth weight babies.
"The fact that the long-term data looks this good is very heartening," said Dr Jill Rabin, chief of ambulatory care, obstetrics and gynaecology at Long Island Jewish Medical Centre in New Hyde Park, New York. "I think parents can take heart and have hope."
"You can really make up what the child didn't get in the beginning from being very low birth weight or premature," Rabin said. "Eventually they do catch up, and are able to be fully functioning adults."
For more on low birth weight and prematurity, visit the March of Dimes.