Context

Progress in neonatology over the past 40 years has led to unprecedented survival rates of extremely preterm infants. Survival of infants considered to be previable in the late 1980s (ie, 26 weeks’ gestation) has now become the rule. At the same time, the limit of viability has continued to shift towards lower gestational ages, reaching 22–23 completed weeks in some countries. Published data on survival rates of extremely preterm infants vary widely between industrialised countries. This systematic review assesses whether variations in national recommendations for the treatment of borderline viable infants might in part be responsible for the observed differences in survival rates.