Half of all extremely premature babies who survive are mentally or physically disabled, a quarter of them severely so, a new study in the New England Journal of Medicine shows.
As daunting as that sounds, it is better than expected.
The lead researcher, Dr. Neil Marlow of the University of Nottingham, England, had expected to find that about 40 percent of such premature babies wind up with severe disabilities.
He studied all 4,004 babies born before the 26th week of pregnancy over 10 months in the United Kingdom and Ireland.
Only 308 survived after being sent home, Marlow wrote in Thursday's edition of the New England Journal of Medicine.
The researchers were able to follow 300 of the children about 2 1/2 years after what would have been their birthdays had they been born at full term. Another six were checked out a year after what would have been their full-term birthday.
The study said 155 had no problems — though some problems caused by prematurity, including hyperactivity and learning and motor difficulties, may not show up until age 5.
Since the babies all were born in 1995, Marlow and his colleagues are about to start another round of assessment this fall, when the children start school.
"This is when it starts to get really interesting," he said in an interview. "We don't have a huge amount of information on this particularly immature group as they get older."
The disabilities shown by the children at age 2 1/2 included general slowness in mental growth, seizures and problems walking, sitting, using their hands, seeing, hearing and communicating.
The chance of disability was no greater for the children born at 22 weeks than those born at 25 weeks — another surprise for the researchers.
"That's quite useful to know," Marlow said. "It means you don't treat them differently."
Boys were more likely than girls to have problems.
Dr. F. Sessions Cole, a professor of pediatrics at Washington University in St. Louis who was not involved in the study, said it is the first report that lets parents know the chances of life for a baby born before 26 weeks, as well as what happens to surviving babies.
He said many parents believe that babies below a certain weight cannot survive.
"Parents in general feel that if there's any chance that any baby's going to be normal, it's going to be their baby," he said. "It'll influence many parents to hope."