Background: Early-term birth (gestational age, 37–38 weeks) has been associated with increased infant mortality relative to later-term birth, but mortality beyond infancy has not been studied. We examined the association between early-term birth and mortality through young adulthood.
Methods: We conducted a national cohort study of 679,981 singleton births in Sweden in 1973–1979, followed up for all-cause and cause-specific mortality through 2008 (ages 29–36 years).
Results: There were 10,656 deaths in 21.5 million person-years of follow-up. Among those still alive at the beginning of each age range, early-term birth relative to those born at 39–42 weeks was associated with increased mortality in the neonatal period (0–27 days: adjusted hazard ratio = 2.18 [95% confidence interval = 1.89–2.51]), postneonatal period (28–364 days: 1.66 [1.44–1.92]), early childhood (1–5 years: 1.29 [1.10–1.51]), and young adulthood (18–36 years: 1.14 [1.05–1.24]), but not in late childhood/adolescence (6–17 years: 0.97 [0.84–1.12]). In young adulthood, early-term birth was strongly associated with death from congenital anomalies and endocrine disorders, especially diabetes (2.89 [1.54–5.43]).
Conclusions: In this large national cohort study, early-term birth was independently associated with increased mortality in infancy, early childhood, and young adulthood. Lowest short-term and long-term mortality was among those born at 39–42 weeks.