Preterm Birth Associated With Diminished Long-Term Survival, Reproduction

An analysis of births in Norway found that persons born preterm had an increased risk of death throughout childhood and lower rates of reproduction in adulthood, compared to persons born at term, according to a study in the March 26 issue of JAMA.1
Preterm birth, defined as birth within 37 weeks after conception, is a leading cause of infant death in the industrialized world, after congenital abnormalities. Disability occurs in 60 percent of survivors born at 26 weeks and in 30 percent of those born at 31 weeks, according to background information in the article. Little is known about the long-term risk of death and overall health among persons born preterm.


Geeta K. Swamy, M.D., of Duke University Medical Center, Durham, N.C., and colleagues conducted a study to determine how preterm birth affects long-term survival, subsequent reproduction and next-generation preterm birth. “Such information may be useful to practitioners caring for families with survivors of preterm birth as well as parents of preterm infants,” the authors write.
The researchers analyzed data from the Medical Birth Registry of Norway for 1,167,506 births from 1967-1988. The group was followed up through 2002 for survival. There was also an analysis for those born from 1967-1976 for assessment of educational achievement and reproductive outcomes through 2004. Of the 1,167,506 births, 60,354 (5.2 percent) were preterm. The percentage born preterm was higher among boys (5.6 percent) than among girls (4.7 percent), which is consistent with the male-dominated sex ratio of all births.


The researchers found that the preterm participants had an increased risk of death throughout childhood. For boys born at 22 to 27 weeks, mortality rates were 1.33 percent and 1.01 percent for early (1 - 5.9 years) and late (6 – 12.9 years) childhood death, with a 5.3 times higher risk for early death, and 7 times higher risk for late childhood death. The mortality rate for girls born at 22 to 27 weeks was 1.71 percent for early childhood death, with a 9.7 times higher risk for early childhood death; there were no late childhood deaths.
For 28 to 32 weeks, the early and late childhood mortality rates among boys were 0.73 percent and 0.37 percent, with higher risks of death of 2.5 times, and 2.3 times, respectively. Girls born at 28 to 32 weeks did not have a significantly increased risk of childhood death.
 
Reproduction during adulthood was diminished for participants born preterm compared to those born at term. For men and women born at 22 to 27 weeks, absolute reproduction was 13.9 percent and 25 percent, with men being 76 percent less likely to reproduce; women, 67 percent less likely. For those born at 28 to 32 weeks, absolute reproduction was 38.6 percent and 59.2 percent for men and women, with lower rates of reproduction of 30 percent, and 19 percent, respectively. Preterm women but not men were at increased risk of having preterm offspring.


“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,” the authors conclude.


In an accompanying editorial, Melissa M. Adams, M.P.H., Ph.D., of RTI International, and Wanda D. Barfield, M.D., M.P.H., of the Centers for Disease Control and Prevention, Atlanta, comment on the findings of Swamy and colleagues.2
“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.”


“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.”


1. JAMA. 2008; 299[12]:1429-1436.
2. JAMA. 2008; 299[12]:1477-1478.