 Combined pH and multiple intraluminal impedance pH-MII is currently considered the best choice for GER diagnosis in preterm infants. While pH monitoring is limited to the detection of acid reflux, combined pH-MII effectively identifies both acid and non-acid GER, which is predominant in preterm infants. Moreover, it allows to evaluate the height reached by the refluxate within the esophageal lumen and to distinguish retrograde fluid bolus movements reflux from the anterograde ones swallows. 