NEC is classified by modified Bell's classification. 21[39] The final determination of the diagnosis of NEC (≧ stage2) is made by two independent attending physicians who did not know the group assignment of the infant. Demographic and clinical variables that are potential risk factors for NEC were prospectively abstracted from the medical records. These factors included chorioamnionitis, prolonged rupture of amniotic membrane (PROM) >18 hours, pre-eclampsia, use of prenatal steroid, multiple -pregnancy, mode of delivery, gender, gestational age, birth weight, small for gestational age, Apgar score at 5 minutes, asphyxia, initial Hb, initial body temperature, use of surfactant, use of indomethacin, dosage of indomethacin, days of UAC and UVC, days of fasting, use of dopamine, days of antibiotics use, days of dopamine use, incidence and grading of IVH, incidence of pneumothorax, days of mechanical ventilation and oxygen supplement, days of TPN before and after NEC; weight gain per week, lengthy of stay are prospectively abstracted from the medical records.