Bronchopulmonary dysplasia (BPD) is one of the most common and severe complications of extreme prematurity, affecting approximately 40% of infants born before 28 weeks of gestation. Despite advances in neonatal care and improved survival rates for extremely preterm infants, the incidence of BPD remains high. BPD is associated with significant short- and long-term morbidity, including chronic respiratory impairment, pulmonary hypertension, recurrent respiratory infections, and neurodevelopmental sequelae. Current diagnosis of BPD is based on the need for respiratory support at 36 weeks postmenstrual age, limiting opportunities for early therapeutic intervention. Since structural lung injury may become irreversible within the first weeks of life, the identification of reliable early predictors of BPD is a major clinical priority. Lung ultrasound (LUS) is a non-invasive, radiation-free, bedside imaging technique increasingly used in neonatal intensive care units. The Lung Ultrasound Score (LUS) provides a quantitative assessment of lung aeration and has demonstrated utility in predicting several neonatal respiratory outcomes. Recent studies suggest that both LUS and pleural line abnormalities detected during the first weeks of life may be associated with the subsequent development of BPD, although evidence remains heterogeneous and no universally validated predictive method is currently available.

Bronchopulmonary dysplasia (BPD) is one of the most frequent and severe complications of extreme prematurity and remains a major cause of neonatal morbidity despite significant advances in perinatal and neonatal care. BPD is associated with long-term respiratory, cardiovascular, and neurodevelopmental complications and continues to affect a substantial proportion of infants born at very low gestational ages. Current diagnostic definitions of BPD rely on the need for respiratory support at 36 weeks postmenstrual age. Consequently, diagnosis is established after the period during which preventive and disease-modifying interventions are likely to be most effective. Evidence suggests that irreversible structural changes of the developing lung may occur within the first weeks of life, making early identification of infants at high risk of BPD a clinical priority. Lung ultrasound (LUS) has emerged as a safe, non-invasive, bedside imaging modality capable of assessing lung aeration and pulmonary abnormalities in preterm infants. The Lung Ultrasound Score (LUS) provides a quantitative evaluation of lung aeration loss and has shown promising results in predicting respiratory outcomes in neonatal populations. In addition, pleural line abnormalities, including thickening, irregularity, fragmentation, and subpleural consolidations, have been associated with the subsequent development of BPD. Although several studies have suggested that lung ultrasound findings obtained during the first two weeks of life may predict BPD, no standardized and universally accepted method for early risk stratification is currently available. Furthermore, the optimal ultrasound parameters and their predictive performance remain uncertain. The first 15 days of life represent a critical window for assessing the risk of BPD and for identifying infants who may benefit from preventive therapeutic strategies before irreversible lung injury develops. The aim of this study is to evaluate whether lung ultrasound findings obtained during the first two weeks of life, including Lung Ultrasound Score and pleural line characteristics, are associated with the subsequent development of BPD and may therefore serve as early prognostic markers. Because two clinical definitions of BPD are currently widely used in clinical practice and research, and no clear evidence has demonstrated the superiority of one definition over the other for diagnostic or prognostic purposes, both the Jobe and Bancalari definition and the Jensen definition will be applied in this study. The primary objective is to evaluate the diagnostic performance of the Lung Ultrasound Score measured at 7 and 14 days of life for the prediction of BPD and moderate-to-severe BPD in preterm infants.

Inclusion Criteria:

• born at less than 32 weeks' gestational age;
• born in the Neonatology Department of one of the centres participating in the study or transferred there from another hospital within the first week of life;
• parents/guardians have signed an informed consent form regarding the inclusion of thenewborn in the study and consent to the processing of personal data

Exclusion Criteria:

• major malformations,chromosomal abnormalities, congenital chest wall deformities, congenital heart defects, pulmonary hypoplasia, diaphragmatic hernia, suspected muscular dystrophy or neurological disorders that may impair lung development;
• receipt of palliative care from birth;
• death before 36 weeks' gestational age;
• inability to perform a chest ultrasound or to adequately examine all 6 lung fields at both 7 (+/-1) and 14 (+/-2) days for any intervening reason;
• inability to collect the data necessary to formulate a diagnosis of BPD within the duration of the study

Consecutive preterm infants born at less than 32 weeks' gestational age and admitted to participating NICUs during the study period.