Introduction: We suspected that the incidence of NEC in Denmark had increased during the last 20 years but hypothesized that this could be explained by the increased neonatal survival.
Methods: We conducted a retrospective, observational cohort study of all registered liveborn infants in Denmark in the period from January 1, 1994 to December 31, 2014. Data were obtained from the Medical Birth Registry, National Patient Register, and Cause of Death register in Denmark. The primary outcome was the registration of NEC (ICD-10: DP77.9) during a hospital admission within 6 months after birth. The statistical analysis used 'death before NEC' as a competing risk.
Results: The cohort consisted of 1,351,675 infants, of which 8,059 died. There was a strongly significant decreasing risk of death over the period for the all infants (p<0.0001 in all gestational age groups). In total, 994 infants were diagnosed with NEC which lead to an incidence of 7.4 per 10,000 live-born infants. During the observation period, the incidence increased from 6.3 to 7.9 per 10,000 births (p = 0.006). When accounting for 'death before NEC' as a competing risk, the increase could be explained by the increased neonatal survival. There was, however, a GA-group/epoch interaction (p = 0.008) in the cause-specific hazard ratios with a trend towards an increasing risk of NEC in the most preterm infants and a decreasing risk of NEC in the term infants.
Conclusion: While the overall incidence of NEC increased over the study period, the overall risk of NEC did not increase when considering the increased survival. Nevertheless, there seemed to be an increased risk of NEC in the most premature infants which was masked by a decreased risk in the term infants. This study suggests that research to prevent NEC in the most preterm infants is more important now than ever.