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Aim: We evaluated the increased centralisation of extremely preterm (EPT) births in Sweden in relation to the changes in mortality and morbidity.

Methods: Population-based data covering Swedish live births from 22 + 0 to 26 + 6 weeks of gestation during 2004–2007 and 2014–2016 were analysed for associations between time-period, birth within (inborn) or outside (outborn) regional centres, and outcomes.

Results: Among 1626 liveborn infants, 703 were born in 2004–2007 and 923 in 2014–2016. Birth outside (vs. within) regional centres was associated with a higher infant mortality even after adjustment for birth cohort, gestational age, birthweight standard deviation score and infant sex (adjusted odds ratio 2.01, 95% confidence interval 1.31–3.07, p = 0.001). The higher 1-year mortality in outborn infants was mainly due to more deaths within 24 h after birth. Outborn infants had a higher incidence of intraventricular haemorrhage grade 3–4 than inborn infants (22% vs. 14% in 2004–2007, and 22% vs. 13% in 2014–2016, both p < 0.05). While survival to 1 year without major morbidity increased in inborn infants (33%–40%, p = 0.008), it remained unchanged in outborn infants (29% vs. 30%, p = 0.88).

Conclusion: Centralisation of EPT births contributed to a lower 1-year mortality in 2014–2016 than that in 2004–2007, attributed to a decrease in deaths before 24 h among inborn infants.