Age at onset of necrotizing enterocolitis. Risk factors in small infants.

We compared the features of 45 infants with early-onset necrotizing enterocolitis (NEC) (in the first ten days of life) and 41 infants with late-onset NEC (after the tenth day of life); all weighed 1,500 g or less at birth. Infants with late-onset NEC were smaller at birth and had younger gestational ages than infants with early-onset illness. No significant differences between the two groups, however, were found in sex or race distribution, mean one- and five-minute Apgar scores, or in the relative frequency of occurrence of 30 maternal and neonatal risk factors. Intravenous alimentation was administered significantly more frequently to infants with late-onset NEC. Birth weight-specific weekly attack rates for NEC declined dramatically when infants reached the equivalent of 35 to 36 weeks' gestational age. We hypothesize that the timing of noxious events in relation to gut maturity may explain these observations.