Very small premature babies born in the late 1970s turned out less intelligent than other youngsters their age, a study found. But to researchers' surprise, they got into less trouble as teens, perhaps because they had doting parents.
As expected, the preemies in the study of Cleveland-area children had learning difficulties and persistent neurological problems while growing up. But they also reported significantly less risky behavior as young adults than a comparison group.
Differences between the groups were found when it came to the use of alcohol, marijuana and other illegal drugs; conviction of a crime or other contact with police; and, for girls, having sex and getting pregnant by age 20.
``That was totally unexpected, because there's a lot of literature that criminality is related to lower IQ,'' said Dr. Maureen Hack, who led the study as director of the neonatal follow-up program at Rainbow Babies and Children's Hospital in Cleveland. She said the researchers thought the preemies would have had more behavior problems.
She said one possible explanation is that the preemies' parents saw their children as particularly precious and watched over them more.
Dr. Henry Shapiro, chairman of the American Academy of Pediatrics' section on developmental pediatrics, said there is no evidence that the hypothesis is correct. But he said the study could help policymakers better plan for the medical and educational needs of premature babies.
Infants of very low birth weight, 3.3 pounds or less, account for 1 percent of all U.S. births, or about 40,000 babies per year.
The babies in the study were born at 29 weeks and just over 2 1/2 pounds on average.
They were born between 1977 and 1979, before neonatal intensive care units and specialized technology were widely used to keep tiny preemies alive. Today, lung treatments, breathing machines, intravenous feeding and other technology enable some preemies as small as a pound to survive, though with significant disabilities.
Hack said her findings would probably apply to many of today's premature infants.
Past research on premature babies found higher rates of learning disabilities such as attention deficit disorder and of neurological problems such as cerebral palsy, blindness and deafness.
Earlier studies generally followed children until school age. This study followed the preemies until age 20 and examined their physical growth, behavior and mental health as well as intelligence.
The research was reported in Thursday's New England Journal of Medicine. It was funded by the National Institute of Child Health and Human Development.
The researchers examined 242 Cleveland-area preemies at age 8 and again at 20, through IQ tests, neurological examinations and questionnaires completed by both the children and their parents. The preemies were compared with 233 area children with normal birth weights.
As expected, the preemies were slightly less likely to have graduated from high school, had somewhat lower IQs, and had higher rates of neurological problems and subnormal height; the preemie men were barely half as likely as their counterparts to be attending college.
But except for cigarette smoking and sexual activity among the males, the preemies got into less trouble as teens.
``Even those with learning problems, they show resilience'' and feel good about themselves, Hack said.
Hack just started a long-term study of babies born at less than 2 pounds from 1992 through 1995 that will study levels of parental monitoring and socializing. She wants to determine why they get into less trouble.