The main hypothesis is that even preterm infants considered stable receiving non-invasive ventilation may be at risk of developing BPD due to an inhomogeneous distribution of ventilation. Identifying this characteristic from the first days of life by using EIT could, in the future, optimize non-invasive ventilation strategies as early as possible, such as lung recruitment manoeuvres, which are currently mainly used during invasive mechanical ventilation. In addition, comparing the LUS scores and homogeneity parameters derived from the EIT may help to further confirm the role of semi-quantitative lung ultrasound as a rapid, non-invasive, and readily available tool in NICUs for monitoring the lung function of preterm infants in the short and long term. The primary objective is to measure homogeneity by Electrical Impedance Tomography (EIT) technology, used in the first weeks of life, for the development of BPD of grade 3, at 36 weeks postmenstrual age or death, in stable preterm infants requiring non-invasive ventilation. The secondary objective are to score if homogeneity at EIT are present and whether if they are associated with BPD. to ompare the distribution of regional lung ventilation obtained by EIT with the validated LUS scores.