Effect of birth weight on the association between necrotising enterocolitis and red blood cell transfusions in ≤1500 g infants

CONTEXT Reports evaluating a possible association between necrotising enterocolitis (NEC) and blood transfusion have been predominantly case-control studies. As the possible associations of disease with any variable on which cases and controls have been matched cannot be explored, a cohort study would offer a solution to this problem. OBJECTIVE Our objective was to evaluate the association between exposure to a packed red blood cell (PRBC) transfusion and development of NEC in a cohort where biases of matching are omitted. DESIGN In a retrospective cohort, exposed infants were defined as those who received a transfusion and did not develop NEC or developed NEC within 48 h of the transfusion. All others were considered unexposed. SETTING A single regional perinatal centre in Memphis, Tennessee, USA. PATIENTS 3060 ≤1500 g birth weights (BW) were included. OUTCOME MEASURES The relative risk of developing NEC after exposure to a PRBC transfusion was measured. RESULTS 3060 infants were identified. 174 infants (5.7%) developed NEC; 116 of the 174 infants (67%) were exposed. NEC infants had a significantly lower BW (924 vs 1042 g) and required a longer stay on a ventilator (7 vs 2 days). Divided into groups, infants with BW ≤750 , 751-1000 , 1001-1250 g and 1251-1500 g (n=52, 51, 46 and 25, respectively) had a relative risk of 0.14, 0.46, 1.83 and 1.78 (p<0.01, 0.02, 0.07 and 0.17), respectively, to develop NEC after an exposure. Infants with longest ventilator days were also significantly less likely to develop NEC after an exposure; relative risk=0.11 (p<0.01). CONCLUSIONS Exposure to transfusions was less likely associated with NEC in ≤1000 g infants and remained a risk factor in 1001-1500 infants. BW has to be factored in any study evaluating the association between PRBC transfusions and NEC.