Inclusion Criteria:  admission to the hospital within 24 hours after birth gestational ages:28-32 weeks requiring TPN during the first days of life  Exclusion Criteria:  major congenital abnormalities, chromosomal abnormality congenital intrauterine infection, genetic metabolic diseases structural liver abnormality surgical treatment was taken during hospitalization with severe symptoms of digestive system disease before TPN incompletion or withdrawal of treatment during hospitalization