In this prospective, observational longitudinal study, infants will undergo clinical and
growth assessment at 6 and 12 months' follow-up. Respiratory complications, such as
wheezing, infections, chronic cough will be recorded along with hospital admissions and
drug prescription or use.

Infants will undergo PFT with the infants in the supine position, during quiet, natural
sleep, according to American Thoracic Society/European Respiratory Society
recommendations with measurement of lung volumes, flow, functional residual capacity,
time to peak tidal expiratory flow/expiratory time ratio (tPTEF/tE)10. Lung ultrasound
will be performed to rule out lung abnormalities. After allowing adaptation to the mask,
the investigators will record tidal breathing, flow volume loops for >2 minutes or >20
artifact-free breaths. Using commercially available software (Spiroware, Ecomedics), the
investigators will extract tidal breathing parameters: ratio of time to reach peak tidal
expiratory flow to expiratory time (tPTEF/tE), tidal volume (VT), and respiratory rate
(RR). tPTEF/tE is a reproducible and reliable marker of airway obstruction, can detect
severe expiratory airway obstruction in infants with respiratory complaints and is
associated with subsequent wheezing in infancy.

Appropriate statistical methods will be used to describe clinical characteristics of
patients and compare groups (T-test, Mann-Whitney test, chi-squared test, multivariate
analysis, mixed models depending on data distribution - evaluated with Shapiro-Wilk test
- and data characteristics).