Background The antioxidant defenses are poorly developed in preterm infants. Oxygen and parenteral nutrition (PN) which is contaminated with peroxides are two major sources of oxidants.

Objective To assess the effect of early oxygen (on day 7 and 28) and the PN duration on oxidative stress markers at 36 weeks post menstrual age (PMA) and on the incidence of neonatal morbidities.

Design/methods A prospective observational study including 120 infants less than 29 weeks gestational age without major congenital anomalies. Consent for blood sample at 36 weeks PMA was obtained for 51 infants. GSH and GSSG (nmol/mg protein) were measured by capillary electrophoresis and were used for redox potential (mV) calculation using Nernst equation, and expressed as mean (± sem). BPD was defined as the need of O₂ supplement at 36 weeks PMA. ROP that required either laser or anti-VGF treatment and NEC grade 2 or higher according to Bell’s criteria were included. Student’s t test or Chi squared were used as appropriate, * = p < 0.05, **= p < 0.01.

Results FiO₂ ≥ 25% on day 7 and 28 of life and PN duration > 14 days resulted in higher GSSG concentration, more oxidised redox potential at 36 weeks PMA and increased the incidence of BPD, ROP and NEC

Conclusions Early life exposure to oxidants is associated with prolonged oxidative stress and higher incidence of neonatal morbidities. These results suggest that strategies targeting judicious O₂ use and either decreasing the duration or using safer formulation PN will help decreasing the incidence of BPD, ROP and NEC.