The diagnostic hypothesis is based on the evidence that, while the functional closure of the PDA (Patent Ductus Arteriosus) occurs within a few hours after birth, anatomical closure may take several weeks. The functional closure of the PDA can be extremely sensitive to variations in blood oxygen tension and the hemodynamic instability of preterm infants. Therefore, echocardiographic evaluation and ductal diameter at a single point in time (such as during PDA echocardiography) may not correlate with transductal blood flow. Assessing the variation in the amount of pulmonary interstitial fluid using LUS (lung ultrasound score) could be an early predictive parameter for the closure or non-closure of hsPDA (hemodynamically significant PDA).