A new study published in JAMA analyzed Norwegian births and concluded that compared to people who were born at term, people who were born preterm were more likely to die during childhood and less likely to reproduce in adulthood.

Babies who are born 37 weeks after conception are classified as preterm. After congenital abnormalities (conditions present at birth), preterm birth is a leading cause of infant death in industrialized countries. Sixty percent of survivors born at 26 weeks and 30 percent born at 31 weeks have some type of disability. This study, conducted by Geeta K. Swamy, M.D. (Duke University Medical Center, Durham, N.C.) and colleagues, seeks to fill the research gap concerning the long-term risk of death and overall health among persons born preterm.

Swamy and colleagues set out to investigate how long-term survival, reproduction in adulthood, and possible next-generation preterm birth are affected by preterm birth. The researchers write, “Such information may be useful to practitioners caring for families with survivors of preterm birth as well as parents of preterm infants.”

The data consisted of 1,167,506 births from 1967-1988 from the Medical Birth Registry of Norway, followed up through 2002 for the survival outcome. For individuals born from 1967-1976, the researchers included an analysis of educational achievement and reproductive outcomes through 2004. Of the total sample, 5.2% were preterm (60,354), and more boys than girls were born preterm – 5.6% of boys and 4.7% of girls.

One key finding was that people who were born preterm had an increased risk of death during childhood. Childhood death is divided into the categories of early (1 – 5.9 years) and late (6-12.9 years). Boys born at 22 to 27 weeks had a mortality rate of 1.33% for early childhood deaths and 1.01% for late childhood death. These preterm boys had 5.3 times higher risk for early death and 7 times higher risk for late childhood death. The outcome for girls is slightly different, with 1 1.71% mortality rate for early childhood deaths and no late childhood deaths. Girls had a 9.7 times higher risk for early childhood death.

Boys born at 28 to 32 weeks had early childhood mortality rates of 0.73% and late childhood mortality rates of 0.37%. These groups had higher risks of death of 2.5 times and 2.3 times, respectively. Contrastingly, girls born during this same time had no significant increase in risk of childhood death.

Studying reproduction in adulthood, the researchers found that people born preterm were less likely to reproduce than people born at term Among people born at 22 to 27 weeks, men had a reproduction rate of 13.9% and women 25%; men were 76% less likely and women were 57% less likely to reproduce. For the group born at 28 to 32 weeks, absolute reproduction rates were 38.6% and 59.2% for men and women, respectively. These men were 30% less likely to reproduce and the women 19% less likely. Additionally, women who were born preterm, but not men, had a higher risk of preterm offspring.

The authors conclude: “In this study population, preterm birth was negatively associated with both long-term survival and reproduction. As the preterm birth survivorship continues to grow, further studies will show whether improvements in obstetric and neonatal care affect survival as well as reproductive capacity and long-term quality of life. Continued research aimed at elucidating causal pathways and better therapeutic approaches are imperative for successful strategies to prevent preterm birth.”

An accompanying editorial adds: “At present, clinicians can extend guarded optimism to the families of children who are born very preterm. The findings of Swamy et al illustrate that the survival of preterm infants-although lower than that of their term peers-improves to adulthood. Nonetheless, compared with their adult term peers, fewer adult preterm survivors reproduce. These risks should be interpreted cautiously because the majority of preterm infants have good health and good reproduction. Norway demonstrates better outcomes than the United States, which has persistent, stark racial disparities.”

The editorial, written by Melissa M. Adams, M.P.H., Ph.D. (RTI International) and Wanda D. Barfield, M.D., M.P.H. (Centers for Disease Control and Prevention, Atlanta), concludes that, “Because lifetime risk of poor health is increased among individuals who were born preterm, patients should inform their clinicians about their history of preterm birth. This information may help clinicians identify and manage childhood and adult chronic conditions. Clearly, population-based data on preterm delivery and its long-term consequences may be pertinent medical history for the nation’s future health.”

Association of Preterm Birth With Long-term Survival, Reproduction,and Next-Generation Preterm Birth
Geeta K. Swamy; Truls Østbye; Rolv Skjærven
JAMA (2008). 299[12]:1429-1436.
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Written by: Peter M Crosta