BAX and necrotizing enterocolitis: In NEC group, the difference of Bax mean from day 1 to day 7 in each organ was statistically significant (F = 3.154, P = 0.017), the difference of PCNA mean from day 1 to day 7 in each organ was statistically significant (F = 5.141, P = 0.001), the difference of PAF mean from day 1 to day 7 in colon and ileum was statistically significant (F = 4.300, P = 0.039), but the difference of PAF mean from day 1 to day 7 in lung, liver and kidney was not statistically significant (F = 2.080, P = 0.121).