The goal of this observational study is to learn about the prevalence and characteristics of functional gastrointestinal disorders (FGID) in at risk infants (former preterm infants and those with birth asphyxia) during the first 2 years of life. The main questions it aims to answer are: * evaluate the prevalence of symptoms related to gastro-esophageal reflux (GER), of functional gastrointestinal disorders during the first 2 years of life * describe growth parameters during follow-up up to the corrected age of 2 years Participants will be assessed clinically and with a structured questionnaire based on the Rome IV criteria to describe FGID.