Due to several promoting factors, gastro-esophageal reflux (GER) is very frequent in preterm infants. To limit the potentially harmful widespread of pharmacological treatment, a step-wise approach, which firstly undertakes conservative strategies, is currently considered the best choice to manage GER in the preterm population. Among the most common conservative strategies, postural measures seem to effectively reduce GER features in symptomatic preterm babies, whereas feed thickening is almost ineffective. Due to their prematurity, preterm infants \<34 weeks gestation are often unable to coordinate sucking, swallowing and breathing, thus requiring a feeding tube to ensure adequate enteral intakes. Continuous feeding and boluses are the most common techniques of enteral tube feeding in Neonatal Intensive Care Units; at present, however, the effects of these techniques on GER features have not been clearly established. This observational, prospective and explorative study primarily aims to evaluate the effect of different techniques of enteral tube feeding on GER frequency and features in symptomatic preterm infants (gestational age ≤33 weeks) undergoing a diagnostic combined pH and multiple intraluminal impedance (pH-MII) for GER evaluation.