March 25, 2008 -- Preterm birth is associated with an increased risk of death throughout childhood and a decreased likelihood of reproducing in adulthood, according to surprising findings from one of the largest studies ever to examine the health implications of premature delivery.
The findings suggest that there are even more long-term health issues associated with being born prematurely than have been previously recognized.
Premature birth is a leading cause of infant death and childhood developmental delays in industrialized countries, but its impact on mortality and health into adulthood has not been well understood.
Long-Term Risks of Preterm Birth
In an effort to address this, researchers from Duke University Medical Center followed Norwegians from birth, tracking gestational age at delivery, mortality, and reproductive outcomes.
Using Norway's national birth registry, the researchers followed 1.16 million people born in the country between 1967 and 1988 for as little as 14 years and as long as 35 years.
Their findings appear in tomorrow's issue of the Journal of the American Medical Association.
The absolute death risk after reaching age 1 was quite low, regardless of gestational age at birth.
But compared to children born full-term, the risk of dying before the age of 6 was found to be almost 10 times higher among girls born extremely prematurely (between 22 and 27 weeks of gestation), and five times higher among boys.
Newborns are considered premature when they are delivered prior to 37 weeks of gestation.
The increased risk of death persisted for extremely premature boys, but not girls, until age 13.
"Pre-term birth is a major cause of infant mortality, so you would expect to find more deaths in the first year of life or even the first couple of years," researcher Geeta K. Swamy, MD, tells WebMD. "But we were surprised to find that the increased risk persisted into childhood and even into adolescence in boys."
Reproduction Rates Much Lower
Reproduction rates were also dramatically lower among men and women born between 22 and 27 weeks of gestation, compared to those born full term.
About 68% and 50%, respectively, of the Norwegian women and men born at term had reproduced by 2004, compared to just 25% of extremely preterm women and 14% of extremely preterm men.
Reproduction rates increased with gestational age, suggesting that the finding was not a matter of chance, Swamy says.
The reasons for the associations seen in the study remain unknown.
And it is not clear if babies born today face the same long-term risks as those identified in the study.
The survival rate among babies born very prematurely continues to increase, thanks to medical advances and aggressive management.
"We have better interventions to help babies survive, but we don't have better interventions to prevent preterm births," Swamy says. "We really need a better understanding of the causes of preterm delivery."
Findings Cause for 'Cautious Optimism'
Research epidemiologist Melissa Adams, PhD, MPH, of the research group RTI International says the study shows the importance of finding better ways to reduce premature delivery.
"Every additional week of gestation is very important for reducing the risk associated with premature birth," she tells WebMD.
In an editorial accompanying the study, Adams and Wanda Barfield, MD, MPH, of the CDC write that the findings should be interpreted cautiously.
Barfield tells WebMD that the mortality findings are cause for "cautious optimism" because the survival disadvantage associated with preterm birth declines with age and the absolute risk of death after infancy is small among people born prematurely.
March of Dimes Medical Director Alan Fleischman, MD, tells WebMD that the prognosis is generally good for babies born at 26 weeks of gestation or more.
Babies born prior to this often have lifelong developmental issues, which can vary from mild to extremely severe.
Because of this, the families of babies born at this threshold of viability need to be fully informed of possible outcomes and involved in decisions about how aggressive to be with medical interventions.
"We have to respect the importance of family involvement in decisions about care for these sickest and smallest children, because their outcomes are so uncertain," he says.