Why birthplace still matters for infants born before 32 weeks: Infant mortality associated with birth at 22-31 weeks' gestation in non-tertiary hospitals in Victoria over two decades

Background Very preterm infants born in non‐tertiary hospitals (‘outborn’) are known to have higher mortality rates compared with infants ‘inborn’ in tertiary centres. Aim The aim of this study was to report changes over time in the incidence of outborn livebirths, 22–31 weeks and infant mortality rates for outborn compared with inborn births. Methods We conducted a population‐based cohort study of consecutive livebirths, 22–31 weeks’ gestation in Victoria from 1990 to 2009. The relationship between birthplace, gestational age, birthweight, sex and infant mortality were analysed by logistic regression. Results There were 13,760 livebirths, 22–31 weeks: 14% were outborn. The proportion of outborn livebirths fell from 19% in 1991 to a nadir of 9% in 1997, but climbed to 17% by 2009. At all times, outborns had higher mortality rates compared with inborns. The overall infant mortality rate was 250.6 per 1000 outborn compared with 113.3 per 1000 inborn livebirths (adjusted odds ratio (aOR) 2.76 (95% CI 2.32, 3.27, P