Mortality rate-dependent variations in the survival without major morbidities rate of extremely preterm infants.

The effects of improved survival of EPT infants on morbidity among survivors remain largely controversial. This retrospective cohort study of the Korean Neonatal Network data investigated whether the mortality rate of 23-24 weeks' gestation was associated with survival without major morbidities in periviable 25-26 weeks' gestation infants. The 2,083 eligible infants with 23-26 weeks' gestation were grouped based on institutional mortality rate (group 1 and 2 ≤50% and >50% mortality rate, respectively, for 23-24 weeks' gestation) and were further divided into 23-24 and 25-26 weeks' gestation subgroups. The mortality rate of 23-24 weeks' gestation infants was significantly lower in group 1 (32.7%) than in group 2 (69.9%). The survival without major morbidities rate for 25-26 weeks' gestation infants was significantly higher in group 1 (31.2%) than in group 2 (18.5%). Antenatal steroid use and Apgar score at 5 min in group 1 were associated with decreased mortality and survival without major morbidities in 23-24 and 25-26 weeks' gestation infants, respectively. In the multivariate analyses, decreased mortality rates in 23-24 weeks' gestation infants were associated with higher survival without major morbidities rates in 25-26 weeks' gestation infants due to decreased bronchopulmonary dysplasia, periventricular leukomalacia, and late-onset sepsis. Evidence-based perinatal and neonatal practices, including antenatal steroid use and better delivery room care contributing to decreased mortality in periviable 23-24 weeks' gestation infants, were associated with lower morbidity and higher survival without major morbidities in more mature 25-26 weeks' gestation infants.