New research reveals what doctors have long known: infants born prematurely are more likely to die during childhood and if they survive, are much less likely to have children of their own in adulthood.

Newborns are considered premature when they are delivered prior to 37 weeks of gestation. According to the study, about one in eight births in the U.S. is premature. Sixty percent of babies born at 26 weeks of gestation have long-term disabilities, such as chronic lung disease, blindness, deafness and neurodevelopmental problems. That number drops to 30 percent for babies born at 31 weeks.

Also, premature births are attributed to growing incidence of assisted reproduction, which often produces twins, triplets, which are more likely to be born prematurely.

Researchers from Duke University Medical Center followed Norwegians from birth, tracking gestational age at delivery, mortality and reproductive outcomes. The study followed 1.16 million people born in the country between 1967 and 1988 for a little as 14 years and as long as 35 years.

The researchers found that the risk of early childhood mortality (between 1 and 6 years old) was 5.3 times higher for boys born between 22 and 27 weeks’ gestation, and the risk of late childhood death (between 6 and 12.9 years old) was seven times higher. For those born between 28 and 32 weeks, the risk of early childhood death was 2.5 times higher, and the late childhood death risk was 2.3 times higher.

Things looked even worse for girls born prematurely. For example, for those born between 22 and 27 weeks, the risk of early childhood death was 9.7 times higher. The good news is that there were no late childhood deaths in girls in this gestational age group. Additionally, there was no increase in mortality rates in childhood in girls between 28 and 32 weeks.

“If you are a parent who has a preterm child, following the first year of life, the mortality risk goes down. But, keep in mind, it's still increased. It's not a cause for significant alarm because the overall rate of mortality is still low, but you need to keep it in mind and make sure you're getting appropriate medical care and surveillance for your child," said study author Dr. Geeta Swamy, an assistant professor of obstetrics and gynecology at Duke University Medical Center.

Also, the study revealed that boys born the most prematurely were 76 percent less likely to reproduce, with only about one in seven having children, while women were 67 percent less likely to reproduce, with one in four having children.

The study 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? asked Dr. Swamy.

The findings of the study “remind us the prematurity is a very significant health problem that lasts a lifetime,” David Adamkin, a representative for the American Academy of Pediatrics, who was not involved in the study, said, according to the USA Today. Adamkin, who is also director of newborn medicine at the University of Louisville School of Medicine, said the study reinforces the need to reduce preterm birth.

But, according to Dr. Swamy “we have better interventions to help babies survive, but we don’t have better interventions to prevent preterm births. We really need a better understanding of the causes of preterm delivery,” she added.

Researchers Melissa Adams and Wanda Barfield say, in an editorial that accompanies the study, doctors might be able to better identify and manage chronic conditions if they know a patient was born prematurely.

The study’s findings are published in the March 26 issue of the Journal of the American Medical Association.