First-Year Mortality in Moderately Preterm and Late Preterm Infants: A National register Study

To investigate first-year mortality and predictors and causes of death in moderately preterm (MP; birth at 32 +0 –33 +6 weeks’ gestation) and late preterm (LP; 34 +0 –36 +6 ) infants compared to very preterm (VP; <32 +0 ) and term (FT; ≥37 +0 -40 +0 ) infants and to establish mortality rates by region, hospital level, and time. 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%), MP and LP infants accounted for 85,9%. Early, late, and postneonatal mortality decreased with advancing gestational age. Despite overall declines, early neonatal mortality remained significantly higher in MP and LP infants than in term infants. Over time, early neonatal mortality decreased only in MP and LP groups, while first-year mortality declined in LP and term infants. Predictors of death in all mortality categories in MP and LP infants 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 MP and LP infants resembled those of FT more than VP infants, with congenital anomalies being the most common, albeit not easily preventable causes of death. MP and LP infants had an elevated risk of early neonatal mortality compared with term infants. 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.