Study Question: In infants who are born at gestational ages of 23 0/7 to 27 6/7 weeks, does lowering the concentration of supplemental oxygen to target an arterial oxygen saturation by pulse oximetry (SpO2)of 85-89% compared with 91-95%, from the day of birth until the baby's first discharge home, increase the probability of survival without severe neurosensory disability to a corrected age of 18 months?

Most extremely preterm babies require supplemental oxygen for several weeks or even months after birth. The goal of oxygen therapy is to achieve adequate oxygen delivery to the tissues without causing oxygen toxicity and oxidative stress. At present, this goal is elusive in very immature infants. Although it is standard practice in modern neonatal intensive care units to monitor arterial oxygen saturations via pulse oximetry, there is insufficient evidence to guide the choice of the upper and lower alarm limits. A rigorous trial with long-term follow up is urgently needed and long overdue to determine whether oxygen exposure can be reduced safely in extremely preterm infants without increasing the risk of hypoxic death or disability.

Inclusion Criteria:

• Gestational age 23 0/7 - 27 6/7 weeks
• Postnatal age < 24 hours

Exclusion Criteria:

• Infant not considered viable (decision made not to administer effective therapies)
• Dysmorphic features or congenital malformations that adversely affect life expectancy or neurodevelopment
• Known or strongly suspected cyanotic heart disease
• Persistent pulmonary hypertension, e.g. associated with pulmonary hypoplasia
• Unlikely to be available for long-term follow-up