Esophageal pH-MII Duration: 12 or 24 Hours?

The results of the 24 hour MII-pH recording will be compared to those from the first 12 hour of the same study. To this end the study investigators will select the first 12 hour of the recording using the manufacturer's software (Diversatek Zvu Advanced GI Diagnostic Software). Published normal reference values will be used to confirm gastroesophageal reflux (GER). Appropriate statistical methods will be used to perform calculations. Subgroup analyses based on preterm birth, presence of bronchopulmonary dysplasia and type of prevalent GER symptom (respiratory or gastrointestinal) will be performed.