 Data are analyzed using IBM SPSS Statistic version 20.0.0 IBM Corporation, IBM Corporation Armonk, New York, United States. Clinical characteristics in the study groups are compared by t-test for continuous variables and chi-square test for categorical variables. Mann-Whitney U test is used to compare abdominal rSO2 patterns in response to the first feed between groups 1 and 2. A multivariate analysis is also performed to assess the effect of possible confounding factors. 