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.
infants with gestational age at birth < 31 weeks
infants with gestational age at birth < 37 weeks and major respiratory or neurologic morbidity
infants with history of perinatal asphyxia
lack of informed consent
diagnosis of congenital or other major gastrointestinal disease (i.e. inflammatory bowel disease, cancer)