CHICAGO -- Children born extremely prematurely, weighing 2 pounds or less at birth, experience significant learning difficulties that persist into their teen-age years, a study found.
The researchers and experts not involved in the study said the findings should make parents, doctors and educators aware of the risks such children face and the need for them to get help early.
Prematurity is on the rise, partly because of an increase in multiple births and in older women having babies. Also, medical advances enable an increasing number of even the tiniest babies to survive.
Premature babies are known to run a higher risk of problems such as cerebral palsy, mental retardation and vision and hearing trouble. The latest findings bolster previous research linking prematurity to more subtle cognitive problems that may be permanent.
"There is no question that these children are at high risk," said Dr. Saroj Saigal, a professor of pediatrics at McMaster University in Hamilton, Ontario, who led the study. "We are raising the awareness that these children are likely to have problems."
She followed 150 premature babies, who were born in Ontario between 1977 and 1982, into their teens. Her study, published in the February issue of the journal Pediatrics, found that academic difficulties that existed at age 8 continued into the teen-age years.
The study is one of the first to follow premature babies into their teens. Saigal said it is not clear whether these youngsters go on to have difficulties in adulthood; more research on that is needed.
Those studied weighed between about 1 pound, 2 ounces and 2 pounds, 4 ounces at birth and were born about two to three months early, "the sickest of the sickest babies that we see," Saigal said.
Their average age was 14 during the most recent follow-up.
Nearly half were receiving special educational assistance, compared with just 10 percent of a control group of children who were not born prematurely but were similar in gender, age and social class. Twenty-five percent had repeated a grade, compared with just 6 percent of the control group.
Fewer than half of the smallest premature children -- those born weighing 1 pound, 9 ounces and under -- scored in the normal range most intelligence and achievement tests.
And while 42 of the teens had nervous-system or sensory disorders such as cerebral palsy, blindness and deafness, even those who didn't scored significantly lower on achievement tests than the control group.
About 11 percent of the nation's 4 million births are premature, which means they occur before the 37th week of pregnancy. That is up from 9 percent a decade ago. The increase is largely attributed to a rise in the use of fertility drugs, which often result in multiple, premature births.
An estimated 1.4 percent of all births, about 56,000 annually, are considered very low birth weight, or less than about 3 pounds, up from 1.2 percent in 1987.
Dr. Maureen Hack, a Cleveland neonatologist who has studied developmental problems in premature babies, said the learning difficulties may be caused by bleeding in the brain, lack of oxygen to the brain and other problems linked to prematurity.
"These things don't go away," Hack said.