Bronchopulmonary dysplasia (BPD), the most common respiratory complication of extremely preterm birth, significantly impacts healthcare with high morbidity and mortality rates. Despite the well-established primordial role of inflammation and oxidative stress in the development of BPD, clinical practice does not incorporate the testing for biomarkers associated with the development of BPD. The diagnosis of BPD based on required respiratory support at 36 weeks PML, stresses the need for an early prediction tool which could identify patients with high levels of these biomarkers. This on its turn, could also improve treatment approaches in clinical practice which are currently mostly supportive or non-specific and do not target underlying pathophysiologic pathways. Secondly, mucin expression aim to play a rol in other respiratory diseases, whereas in BPD only the potential role of MUC1 was explored. Thirdly, the composition of the airway microbial composition of an infant is assumed to be influenced by different factors. From early on in pregnancy the airway microbiome of the infant is formed, offering a protective role against pathologies. On the other hand, the role of the airway microbiome in the development of BPD remains unclear and needs to be elucidated. The threefold aim of this study is as follows: I. The development of a non-invasive breath test that allows early detection of bronchopulmonary dysplasia, using the potential of VOCs in exhaled breath as biomarkers for inflammation and oxidative stress. II. The exploration of the composition and diversity of the airway microbiome in infants with BPD, their association with exhaled VOCs and the exploration of the placental and vaginal microbiome. III. The detection of potential alterations in airway mucin expression in BPD patients. Through this comprehensive approach, we seek to gain a deeper understanding of how these mutual associations may contribute to the later development of BPD. In total 140 preterm infants, including 70 BPD patients and 70 preterm controls, born below 30 weeks' gestation at the Antwerp University Hospital will be included.