Effect of Early Oral Triple Viable Bifidobacterium Intestinal Flora in Preterm

Preterm infants are at high risk of deeding intolerance especially low birth weight infants, Whether oral triple viable Bifidobacterium and early Micro-feeding may improve the symptoms of feeding intolerance. 84 preterm infants BW(birth weight) less than 2.5kg,entered neonatal intensive care unit(NICU) less than 24 hours and meet the Inclusion Criteria of this study will be Randomly divided into three groups, control group、 treatment group1 (Triple viable Bifidobacterium 0.5g bid po)、treatment group2 （Triple viable Bifidobacterium 0.5g bid po and early micro-feeding）. treatment period for more than 1 week. For three groups, feeding symptoms,the traits and frequency of stool of 3 days,1 weeks,2 weeks.And the stool flora measured by PCR.