Preterm birth and low gestational age has been associated with an increased risk of mortality in early adulthood. However, recent developments in the treatment of preterm birth have largely improved the survival outcomes of preterm survivors. This study aims to evaluate the risk of mortality from infancy into mid-adulthood in preterm survivors.

This national cohort study included a total of 4,296,814 singleton live births in Sweden. The participants were followed up for mortality (maximum age 45 years), and Cox regression was used to determine the risk of all-cause and cause-specific mortality in relation to gestational age at birth. The primary outcome of the study was all-cause and cause-specific mortality.

During 103.5 million person-years of follow-up, a total of 43,916 (1.0%) deaths were reported. The findings suggested that gestational age at birth was inversely associated with mortality from infancy to mid-adulthood. The adjusted hazard ratios for mortality associated with gestational age at birth were 66.14 for extremely preterm (22-27 weeks), 8.67 for very preterm (28-33 weeks), 2.61 for late preterm (34-36 weeks), and 1.34 for an early term (37-38 weeks).

The research concluded that preterm and early term birth was associated with an increased risk of mortality from infancy to adulthood.