MATERIALS AND METHODS
We conducted a cross-sectional, multicenter study at 11 hospitals from 5
Spanish regions. The study was sponsored by the Working Group of
Perinatal Respiratory Diseases of the Spanish Society of Pediatric
Pulmonology and was approved by the ethics committees at each
participating institution. Written consent was obtained from the
adolescents and their parents/caregivers after providing a full
explanation of the study protocol. The inclusion period was from May
2017 to June 2019.