Preterm infants show mortality risks as children, adults

Infants born prematurely face a higher risk of dying in early adulthood than babies born at full term, researchers report. The higher mortality risk also shows up earlier in life, when the preterm babies are preschool age, scientists report in the Sept. 21 Journal of the American Medical Association.

The study is among the first to gauge the effects of preterm birth on mortality in a large population of adults, says Saroj Saigal, a neonatologist at McMaster University School of Medicine in Hamilton, Ontario, who wasn’t involved in the research. “This is an extremely important paper. It shows that prematurity has lifelong implications.”

The researchers analyzed a birth registry of more than 670,000 people born in Sweden from 1973 to 1979 and matched that information with the country’s death registry through 2008. The scientists took note of the gestational age of nearly 28,000 preterm babies, defined as births occurring less than 37 weeks after a woman’s last menstrual period (full term in this study was defined as 37 to 42 weeks), and tracked the progress of all children who survived past one year. 

Preterm children were 59 percent more likely to die between ages 1 and 5 and 38 percent more likely to die between 18 and 36 than were full-term babies, says study coauthor Casey Crump, a family medicine physician at Stanford University Medical School, who teamed with researchers at Lund University in Sweden for the study. From ages 6 to 17 the groups showed no mortality difference.

Babies born very prematurely had the greatest mortality risk. Each week of prematurity increased a person’s young-adulthood mortality risk by about 4 percent.

Health problems typically seen in babies born prematurely explained some of the higher mortality rates in the preterm group, including lung ailments and heart and hormone irregularities, the registry data indicated. Neurological problems weren’t implicated. “It will be important to inform preterm survivors, their families and physicians to be aware of the long-term health risks,” Crump says.

Saigal notes that signs of higher blood pressure and insulin resistance, an early warning sign of diabetes, are now showing up in studies of people who were born very prematurely, which may increase their mortality risk.

About 5 percent of the births in Sweden in the 1970s were preterm, a rate that’s just over 6 percent now. The U.S. rate is currently about 12 percent. Advances in neonatal care have helped many more of these preemies survive today, some with a gestational age as low as 23 weeks. Such newborns rarely survived in the 1970s when this study began, Saigal says.

The increasing survival of premature infants makes it difficult to apply these findings of mortality risk in adulthood to today’s newborn population.  An infant’s medical care “will always be out of date by the time you do the calculations,” Saigal says.