Study subjects

This is a retrospective cohort study that examined very premature liveborn infants with <30 weeks of gestation at the Zurich University Hospital, a tertiary perinatal centre, from 1 January 2000 to 31 December 2013. Exclusion criteria were a priori palliative care in delivery room, major congenital anomalies (ie, genetic anomaly, syndrome or malformation of a major organ system); dead before hospital discharge; transfer to another centre within the first day of life and insufficient documentation. We extracted neonatal and follow-up data from the prospective national database of the Swiss Neonatal Network. Specific information concerning the severity of BPD according to the 2000-NICHD consensus³ at 36 and 40 weeks’ PMA was extracted from the neonatal charts.