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 will undergo clinical assessment at 3, 6, 12, 24 months' corrected age at the local Follow-up clinic.

Clinical examination, anthropometric measurement and data from a structured questionnaire to detect FGID will be performed.

Z-scores for weight, length and head circumference will be calculated according to the World Health Organization (WHO) standards.

Data from the questionnaires will be collected. Clinical characteristics of patients and perinatal data will be collected and analyzed by appropriate statistical methods.

The prevalence and characteristics of FGID in the study population will be compared to published data (mostly from term infants).

Inclusion Criteria:

• 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

Exclusion Criteria:

• lack of informed consent
• diagnosis of congenital or other major gastrointestinal disease (i.e. inflammatory bowel disease, cancer)

Infants matching the inclusion criteria will be enrolled in the local Follow-up program (as per clinical routine of the local Institution).