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Aim: The definition of necrotising enterocolitis (NEC) is based on clinical and radiological signs that can be difficult to interpret. The aim of the present study was to validate the incidence of NEC in the Extremely Preterm Infants in Sweden Study (EXPRESS)

Methods: The EXPRESS study consisted of all 707 infants born before 27 + 0 gestational weeks during the years 2004–2007 in Sweden. Of these infants, 38 were recorded as having NEC of Bell stage II or higher. Hospital records were obtained for these infants. Furthermore, to identify missed cases, all infants with a sudden reduction of enteral nutrition, in the EXPRESS study were identified (n = 71). Hospital records for these infants were obtained. Thus, 108 hospital records were obtained and scored independently by two neonatologists for NEC.

Results: Of 38 NEC cases in the EXPRESS study, 26 were classified as NEC after validation. Four cases not recorded in the EXPRESS study were found. The incidence of NEC decreased from 6.3% to 4.3%.

Conclusion: Validation of the incidence of NEC revealed over- and underestimation of NEC in the EXPRESS study despite carefully collected data. Similar problems may occur in other national data sets or quality registers.

OBJECTIVE: To investigate potential risk factors behind the increased incidence of necrotising enterocolitis (NEC) in Swedish extremely preterm infants.

DESIGN: Registry data from two population-based national cohorts were studied. NEC diagnoses (Bell stage ≥II) were validated against hospital records.

PATIENTS: All liveborn infants <27 weeks of gestation 2004-2007 (n=704) and 2014-2016 (n=895) in Sweden.

MAIN OUTCOME MEASURES: NEC incidence.

RESULTS: The validation process resulted in a 28% reduction of NEC cases but still confirmed a higher NEC incidence in the later epoch compared with the earlier (73/895 (8.2%) vs 27/704 (3.8%), p=0.001), while the composite of NEC or death was lower (244/895 (27.3%) vs 229/704 (32.5%), p=0.022). In a multivariable Cox regression model, censored for mortality, there was no significant difference in early NEC (0-7 days of life) between epochs (HR=0.9 (95% CI 0.5 to 1.9), p=0.9), but being born in the later epoch remained an independent risk factor for late NEC (>7 days) (HR=2.7 (95% CI 1.5 to 5.0), p=0.001). In propensity score analysis, a significant epoch difference in NEC incidence (12% vs 2.8%, p<0.001) was observed only in the tertile of infants at highest risk of NEC, where the 28-day mortality was lower in the later epoch (35% vs 50%, p=0.001). More NEC cases were diagnosed with intramural gas in the later epoch (33/73 (45.2%) vs 6/26 (23.1%), p=0.047).

CONCLUSIONS: The increase in NEC incidence between epochs was limited to cases occurring after 7 days of life and was partly explained by increased survival in the most extremely preterm infants. Misclassification of NEC is common.

BACKGROUND: In Sweden, the incidence of necrotising enterocolitis (NEC) in extremely preterm infants has increased from 6 to10% over a decade. We examined whether changes in enteral nutrition during the first 2 weeks were associated with growth and development of NEC.

METHODS: The EXPRESS (2004–2007) and EXPRESS 2 (2014–2016) cohorts included infants <27 gestational weeks. NEC diagnoses were validated. Nutritional data were retrieved from four of the six healthcare regions (n = 815). Growth and NEC incidence were compared between cohorts, and odds ratios (OR) were adjusted for early risk factors in a logistic regression model.

RESULTS: In EXPRESS 2, during the first postnatal week, feeding advancement was more rapid (10 vs. 8 ml/kg/d, p < 0.001) and fortification more common (27% vs. 3.6%, p < 0.001). Growth improved from birth to 28 days (delta z-scores: weight, –2.18 vs. –1.49,p < 0.001; length, –2.22 vs. –1.96, p = 0.013) and to 36 weeks’ postmenstrual age. Neither feeding advancement nor fortification was associated with increased NEC risk >7 d (n = 44; aOR 0.96, 95% CI 0.91–1.01, p = 0.15; aOR 1.33, 95% CI 0.57–2.79, p = 0.50).

CONCLUSION: A more active early enteral nutrition policy in Sweden was associated with faster feeding advancement, earlier fortification, increased protein intake, and improved growth without increased NEC risk.