Among nearly 5 million births studied, 6.9% were preterm, with those born extremely preterm (before 28 weeks) found to have an 11.61-fold higher risk of dying in the first year of life compared to those born at full term, according to a recent study.

The cohort study examined the long-term mortality risk in patients born preterm, following 4 998 560 live births in Canada from 1983 to 1996. Of these births, 0.3% occurred at 24-27 weeks' gestation, 0.6% at 28-31 weeks, 0.8% at 32-33 weeks, and 5.1% at 34-36 weeks. During a median follow-up period of 29 years, 72 662 individuals died (14 312 born preterm and 58 350 born at term).

The study found that preterm birth (PTB), defined as birth before 37 weeks of gestation, is associated with a higher risk of mortality from birth to age 36. The highest mortality risk was observed during infancy and early childhood, particularly among those born at the earliest gestational ages, with a gradual decline in risk as patients aged.

Among the study cohort, preterm birth, particularly at earlier gestational ages, was associated with an increased risk of death across all age intervals, with the highest risks seen in those born at 24 to 27 weeks. The greatest risk was observed during the first year of life, with an increased mortality rate of 11.61 times (risk difference [RD], 2.29% [95% confidence interval (CI), 2.23%-2.35%]) for preterm infants compared to those born at term. In early childhood (ages 1-5), the risk remained elevated (RR, 2.79 [RD, 0.34% {95% CI, 0.31%-0.36%}]). While the risk of mortality declined with age, reaching its lowest point between ages 18-28 years (RD, 0.07% [95% CI, 0.04%-0.10%]; RR, 1.13 [95% CI, 1.07-1.19]), it persisted into adulthood, with a modest increase in the risk of death after age 30.

The study, published in JAMA Network Open, identified higher mortality risks from several causes, including respiratory, circulatory, digestive system disorders, infections, and congenital malformations, with risks increasing as gestational age decreased. Notably, no associations were found for external causes of deaths. The researchers noted that some of these associations may have been partly due to underlying health determinants that affected both PTB and mortality.

Full disclosures can be found in the published study.