First-Year Mortality in Infants Born Moderately Preterm and Late Preterm: A National Register Study.

Objective: To investigate first-year mortality and predictors and causes of death in infants born moderately preterm (MP; birth at 32 Study design: Data on all infants (n = 1 546 787) born in Finland between 1991 and 2016 were collected from national registers. Of those born prematurely (5.9%), infants born MP and LP accounted for 85,9%. Results: Early, late, and postneonatal mortality decreased with advancing gestational age. Despite overall declines, early neonatal mortality remained significantly greater in infants born MP and LP than in infants born at term. Over time, early neonatal mortality decreased only in MP and LP groups, whereas first-year mortality declined in infants born MP and LP. Predictors of death in all mortality categories in infants born MP and LP included small for gestational age, low Apgar score, and ventilator treatment. Some regional and hospital-level differences in early neonatal mortality were observed. Causes of death in infants born MP and LP resembled those of term more than infants born very preterm, with congenital anomalies being the most common, albeit not easily preventable causes of death. Conclusions: Infants born MP and LP had an elevated risk of early neonatal mortality compared with infants born at term. Continued reductions may be achieved by targeting preventable causes such as asphyxia and respiratory distress, while counseling-based interventions may help prevent sudden infant death syndrome and reduce late neonatal and postneonatal mortality.