Children who are born prematurely are at increased risk of death well past the toddler years, and are significantly less likely to have children of their own.

In the largest-ever study to document the long-term effects of preterm birth, researchers at Duke University Medical Center analyzed data from 1.2 million Norwegian births, including about 60,000 premature infants.

The results were published Wednesday in the Journal of the American Medical Association, and shed light on the long-term prognosis of premature babies, many of whom survive despite being born with undeveloped lungs, eyes, hearts and skin.

"We have many more survivors but we have many more survivors with some degree of health problems," said Dr. Kate Veness-Meehan, a neonatologist at UNC Hospitals in Chapel Hill who was not involved in the study.

The findings come at a time when more babies are born preterm. That figure has been rising steadily over the past 25 years. Now, 12.8 percent of babies nationally, and about 13.6 percent in North Carolina, are born too early, according to the March of Dimes, which fights birth defects. Doctors don't fully understand the reasons for the rise in prematurity.

Medical breakthroughs, such as the use of special lubricants that help preemies' fragile lungs function better, mean infants that once would have died in the hospital are now living. Lung problems, impaired vision, and physical and developmental delays remain common complications.

And many babies don't survive; premature birth is the leading cause of infant mortality in babies younger than 1 year old, with the highest death rates occurring among the earliest preemies. But little data has been available about risks in late childhood or adulthood.

The Duke study found that death rates were higher among girls born early up until age 5; in boys, the risk of death was higher up until age 13. Researchers did not look at reasons for the childhood deaths.

Also, the number of infant deaths was very small. Even among the earliest preemies -- those born with less than 27 weeks of gestation compared to a full term of at least 37 weeks -- only about 1 percent of girls died by age 5. Deaths among girls carried to full term occurred at a tiny fraction of that rate.

"It's certainly nothing that should be cause for alarm," lead author Dr. Geeta Swamy, who practices high-risk obstetrics at Duke, said of the increased death rates. "But it's important for parents to understand they may have problems down the road."

Physicians and public health experts cautioned that the findings in the Duke study may not apply generally to the United States, which is more racially and socioeconomically diverse than Norway. Also, the births analyzed occurred between 1967 and 1988 -- well before modern medical advances that now increase survival rates among preemies.

Still, Melissa M. Adams, a public health expert and scientist at RTI International, wrote in an editorial accompanying the JAMA study that the findings offer some optimism for preterm babies and their families. She also noted that patients should tell their medical providers if theirs was a premature birth.

"This information may help clinicians identify and manage childhood and adult chronic conditions," wrote Adams, who is based in Atlanta.

Duke researchers also observed that being born early had a significant effect on reproduction, especially among the earliest preemies, though they could not say why. Just 25 percent of the earliest preemie girls had children of their own, compared with about 68 percent of full-term girls. Girls who were born prematurely were also significantly more likely to deliver early. Among boys, the gap was even wider. Just 13 percent of boys born between 22 and 27 weeks of gestation fathered children; more than half of full-term boys became parents.

Born at 26 weeks

Betty Marrow-Taylor of Durham was convinced her son Ezekiel "Zeek" Taylor would suffer profound disability when he was born 26 weeks into her pregnancy in January 1999. The placenta detached from Marrow-Taylor's uterus, forcing her to have an emergency Caesarean section.

"I was sure he was going to have cerebral palsy, blindness -- all those things that can happen with a 26-weeker," Marrow-Taylor said.

Zeek was one of the lucky ones. He had to have surgery to close a hole in his heart, laser surgery to treat eye problems associated with early birth and procedures to correct serious reflux, which is common among preemies. But today, at age 9, Zeek has normal vision, is outgoing and active, and tests at or above grade level in all subjects at school. He has no physical impairments.

"I'm just so grateful that it turned out that way," Marrow-Taylor said. A cousin's experience a few years ago was starkly different. Her daughter, also born at 26 weeks, died of complications before leaving the hospital. "I've seen the other side."