Objective To report the population-based, gestational age (GA)-stratified mortality and morbidity for very preterm infants over 13 years in Switzerland.

Design A prospective, observational study including 95% of Swiss preterm infants (GA <32 weeks) during three time periods: 2000–2004 (P1), 2005–2008 (P2) and 2009–2012 (P3).

Setting The Swiss Neonatal Network, covering all level III neonatal intensive care units (NICUs) and affiliated paediatric hospitals.

Patients 8899 live-born preterm infants with GA <32 weeks.

Main outcome measures Trends in GA-specific mortality (overall, delivery room and NICU), ‘survival free of major complications’ and major short-term morbidities: bronchopulmonary dysplasia (BPD, oxygen requirement at 36 weeks), grades 3 and 4 intraventricular haemorrhage (IVH 3–4), necrotising enterocolitis (NEC) and cystic periventricular leukomalacia (cPVL).

Results Survival rate was 84.4%; 5.7% died in the delivery room and 9.9% died in the NICU. Neonatal mortality was 8.6% and post-neonatal mortality in NICU admissions was 1.3%. Reductions were observed in overall mortality from 18.4% (95% CI 17.0% to 19.8%) in P1 to 13.8% (13% to 15%) in P3, NICU mortality from 12.6% (11.4% to 13.8%) to 8.2% (7.2% to 9.2%) and IVH 3–4 from 7.8% (6.8% to 8.7%) to 5.8% (4.9% to 6.6%). There was no change in the incidence of cPVL and NEC. The BPD (oxygen requirement at 36 weeks) incidence displayed a U-shaped distribution across the three time periods. Overall, 71.0% (70.0% to 72.0%) had ‘survival free of major complications’ at the time of hospital discharge, and this significantly improved from 66.7% (65.0% to 68.4%) to 72.4% (70.8% to 74.0%) between P1 and P3.

Conclusions Survival rates of very preterm infants increased with decreasing delivery room and neonatal mortalities, mostly in extremely preterm infants. The incidence of IVH 3–4 decreased, whereas the incidences of cPVL, NEC and BPD (oxygen requirement at 36 weeks) remained largely unchanged from 2000 to 2012 in Switzerland.