Infants born prematurely are much more likely to die during childhood and, if they survive, much less likely to have children of their own in adulthood, according to the largest study of prematurity ever undertaken.

Researchers already knew that premature infants faced many neurological and developmental problems, but the new findings, released today, indicate that the spectrum of problems is even broader than suspected and persist throughout the child’s lifetime.

The study, conducted using Norwegian birth data, suggests that, as the percentage of premature infants who make it through their first year continues to grow because of advances in neonatology, the number of troubled infants and adults will also rise.

“Are we improving their survival at the expense of significant problems down the road?” the lead author, Dr. Geeta Swamy of the Duke University Medical Center, asked. Experts said the situation is probably worse in America. “Norway demonstrates better outcomes than the United States, which has persistent, stark racial disparities” in care for the premature, Melissa M. Adams of RTI International in Atlanta and Dr. Wanda D. Barfield of the Centers for Disease Control and Prevention wrote in an editorial accompanying the report in the Journal of the American Medical Association.

One in eight infants born in America are premature, a total of more than half a million year, despite the best efforts of physicians to bring more pregnancies to full term — defined as 38 weeks or longer.

Researchers are not sure why America’s rate is so high, but contributing factors include the growing incidence of assisted reproduction, which often produces twins or triplets, which are more likely to be born prematurely.

There is also a rising incidence of deliberately induced premature deliveries and Cesarean sections — many because of distress to the mother or infant, but some for the convenience of doctor or mother.

The consequences can be devastating, particularly for very early births. They include learning disabilities, neurological problems, lung diseases, and cerebral palsy. Using Norway’s extensive registry of births and medical care, Dr. Swamy and her colleagues studied nearly all 1.2 million singleton births in that country between 1967 and 1988, following the children through 2002. They also looked at educational achievement and reproduction in the group born between 1967 and 1976.

A total of 5.2% of the births were premature, less than half the percentage in America.

For boys born the most prematurely, between 22 and 27 weeks, their risk of death was 5.3 times normal between the ages of 1 and 6, and seven times normal between 7 and 13. For boys born between 28 and 32 weeks, the risk of death was 2.5 times normal in early childhood and 2.3 times normal in late childhood.

The most premature girls had 9.7 times the normal risk of death between ages 1 and 6, but no increased risk between 7 and 13. Girls born between 28 and 32 weeks did not have a significantly increased risk of death.

The investigators are not sure what accounts for the increased risk, but some of it is due to cancer and congenital abnormalities, Dr. Swamy said.

In adulthood, boys born the most prematurely were 76% less likely to reproduce, with only about one in seven having children. Women were 67% less likely to reproduce, with one in four having children.

Preterm women, but not preterm men, were at increased risk of having premature offspring.

Those who were born prematurely were also significantly less likely to finish high school or to complete college studies.