We calculated differences of Z-scores for weight, length and head circumference measured at hospital discharge and at birth for each patient (Δ= hospital discharge - birth). Simple and multiple linear regression models were adjusted to compare the three groups in terms of Δ Z-score for the anthropometric measurements. For all multiple models, we considered covariates such as bronchopulmonary dysplasia, peri-intraventricular hemorrhage, SNAPPE II (Score for Neonatal Acute Physiology with Perinatal extension-II), weight and gestational age at birth, occurrence of necrotizing enterocolitis and sepsis. Estimates of the differences among group means and their respective 95% confidence intervals were obtained using the SAS 9.3 software (SAS Institute Inc., USA).