September 20, 2011 — Low gestational age (preterm birth) was associated with a higher risk for death in early childhood and young adulthood, according to a Swedish national cohort study published online September 20 in the Journal of the American Medical Association.

The study is the first "to report the specific contribution of gestational age at birth on mortality in adulthood," write the authors, led by Casey Crump, MD, PhD, from the Department of Medicine, Stanford University, California. Given that prematurity is a huge problem in the United States, they argue that is essential to better understand the "persistent long-term health sequelae of preterm birth."

With the number of preterm births rising, and large numbers of these children surviving to adulthood, better understanding of long-term outcomes is critically important to "enable earlier prevention, detection, and treatment of the long-term health sequelae," the authors add.

The study was specifically aimed at examining the association between gestational age younger than 37 weeks and all-cause and cause-specific mortality. Using data from the Swedish Birth Registry and the Swedish Death Registry, investigators analyzed long-term outcomes from 674,820 individuals born as singletons throughout Sweden between 1973 and 1979 who survived to age 1 year. Preterm births totaled 27,979 (4%). Follow-up continued to 2008 (ages 29 - 36 years). Registry data are nearly 100% complete in Sweden.

Preterm births during the study period accounted for 5% of all births. Analyzing deaths that occurred between age 1 year, through follow-up, to between 29 to 36 years, all-cause mortality data revealed that 7095 deaths occurred in 20.8 million person-years of follow-up.

All death rates were adjusted for sex, birth year, fetal growth, birth order, maternal age at birth, maternal marital status, and maternal and paternal education. For each additional week of gestation, children alive between ages 1 and 5 years gained an 8% survival advantage (P < .0001). Similarly, for patients alive in the age 18- to 36-year group, each additional week of gestation resulted in a 4% survival advantage (P < .001).

Analysis of cause-specific mortality revealed that deaths in early childhood (age 1 - 5 years) were strongly associated with mortality from congenital anomalies, usually heart defects, endocrine disorders, or respiratory disorders. The only other age group showing a strong inverse relationship between gestational age at birth and these same causes was found for young adults (ages 18 - 36 years).

Although late deaths (beyond infancy) were the primary focus of the article, data on deaths during the first year of life revealed an inverse relationship between deaths and gestational age, with 70.7% of those born at 22 to 27 weeks' gestation dying in the first year of life, 18.4% of those born at 28 to 33 weeks' gestation dying in the first year, and 3.1% of those born at 34 to 36 weeks' gestation dying in the first year. These death rates contrast sharply with babies born full term. Approximately 0.7% of those born full-term (37 - 42 weeks' gestation) and 1.0% of those born at 43 weeks' gestation or later died during the first year of life.

The study was supported by grants from the National Institute of Child Health and Human Development, the Swedish Research Council, and the Swedish Council for Working Life and Social Research. The authors have disclosed no relevant financial relationships.

JAMA. Published online September 20, 2011.