Early-term birth (37-38 weeks) and mortality in young adulthood

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.

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).

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]).

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.