GSTM1 and digestive system disorder: To identify factors associated with ID/IDA in the case of daily iron supplementation among premature infants, multivariable logistic regression analysis was performed, with GA, BW, Hb (lowest value during neonatal period, and the values tested at birth, before discharge and at 3 months), sex, maternal complications, neonatal digestive system diseases, intracranial hemorrhage, neonatal history of external iron sources and blood transfusion, growth velocity and feeding patterns as covariates.