Background <p>Recognizing which premature infants are at higher risk of developing BPD/death is a challenge in neonatology. The aims of our study are to identify mitochondrial haplogroups and quantify circulating cell-free mitochondrial DNA (ccf-mtDNA) levels in very preterm infants at risk of bronchopulmonary dysplasia (BPD) or death and explore the relationship between these variables and the development of BPD/death.</p> Methods <p>Single-center prospective cohort study including preterm infants of ≤32 weeks gestational age (GA) and birth weight ≤1500 g. Clinical variables, mitochondrial haplogroups, and ccf-mtDNA levels were determined. Subsequently, diagnosis and staging of BPD/death were performed, and groups were compared.</p> Results <p>The population consisted of 107 newborns (mean GA 28.73 ± 2 weeks; mean birth weight 1,121 ± 332 g). A total of 44 patients (41.1%) presented the outcome of BPD/death without differences in haplogroup distribution and ccf-mtDNA levels between those who survived without BPD (controls). Variables independently associated with BPD/death included GA (<i>p</i> &lt; 0.001; OR = 0.36 [95%CI 0.23–0.5]), birth weight (<i>p</i> &lt; 0.001; OR = 0.99 [95%CI 0.99–0.99]), maximum FiO₂ in the delivery room (<i>p</i> = 0.001; OR = 1.07 [95%CI 1.03–1.12]), hours on mechanical ventilation (<i>p</i> = 0.02; OR 1.02 [95%CI 1.00–1.02]), and postnatal corticosteroids (p &lt; 0.001; OR = 47.12 [95%CI = 5.98–371.1]).</p> Conclusion <p>This is the first study to characterize mtDNA haplogroups and ccf-mtDNA in very preterm infants at risk of BPD/death. None of the mitochondrial variables studied were associated with BPD/death. Further research is needed to elucidate the role of mtDNA in BPD.</p> Impact statement <p><UnorderedList Mark="Bullet"> <ItemContent> <p>Despite advances in perinatal care, bronchopulmonary dysplasia continues to be the most common chronic pulmonary morbidity associated with prematurity.</p> </ItemContent> <ItemContent> <p>Prediction of BPD in early stages is crucial to improve BPD rates, but this remains a major challenge in neonatal units.</p> </ItemContent> <ItemContent> <p>Given that mitochondria play an important role in the inflammatory and oxidative stress responses, we aimed to explore the relationship between mitochondrial haplogroups, circulating cell-free mitochondrial DNA levels, and BPD.</p> </ItemContent> <ItemContent> <p>This is the first work carried out in very preterm infants where mitochondrial haplogroups and the levels ccf-mtDNA are investigated with the intention of discovering a new biomarker for BPD.</p> </ItemContent> </UnorderedList></p>