BackgroundImpaired intestinal microcirculation seems to play an important role in the pathogenesis of necrotizing enterocolitis (NEC). A previous study showed that a SrSO2< 30% is associated with an increased risk of developing of NEC. We aimed to determine the clinical usefulness of the cut off < 30% for SrSO2in predicting NEC in extremely preterm neonates.MethodsThis is a combined cohort observational study. We added a second cohort from another university hospital to the previous cohort of extremely preterm infants. SrSO2was measured for 1–2 h at days 2–6 after birth. To determine clinical usefulness we assessed sensitivity, specificity, positive and negative predictive values for mean SrSO2< 30. Odds ratio to develop NEC was assessed with generalized linear model analysis, adjusting for center.ResultsWe included 86 extremely preterm infants, median gestational age 26.3 weeks (range 23.0-27.9). Seventeen infants developed NEC. A mean SrSO2< 30% was found in 70.5% of infants who developed NEC compared to 33.3% of those who did not (p = 0.01). Positive and negative predictive values were 0.33 CI (0.24–0.44) and 0.90 CI (0.83–0.96), respectively. The odds of developing NEC were 4.5 (95% CI 1.4–14.3) times higher in infants with SrSO2 < 30% compared to those with SrSO2≥30%.ConclusionsA mean SrSO2cut off≥30% in extremely preterm infants between days 2–6 after birth may be useful in identifying infants who will not develop NEC.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12887-023-04145-4.