Bronchopulmonary dysplasia (BPD) is a common, major complication of premature birth, associated with developmental and health consequences that continue into adulthood. Prediction of who will have these problems is challenging using traditional definitions of disease. It is believed that underdevelopment and injury occur in both lung tissue and the blood vessels in the lungs, with a sophisticated interplay between them that contributes to lung disease seen in prematurity. New magnetic resonance imaging (MRI) techniques can delineate tissue structure with unprecedented granularity, assessing lung tissue, blood vessels, and their interplay. The ability to identify, at an early stage, those infants destined for chronic lung disease with greater certainty will be useful in counseling families and critical for the effective introduction of promising new BPD therapies. 319 infants born less than 29 weeks gestation will be recruited from 4 centres, including 5 babies who received stem cell therapy in a clinical trial. Babies will be evaluated at 36 weeks post-conception with lung MRI, oscillometry (lung function), echocardiogram (heart ultrasound), and oscillometry. Lung health will be assessed every 3 months by phone questionnaire and chart review. At 18-21 months post-conception, babies will undergo neurodevelopmental assessment and lung function testing. The investigators will look at how well baseline MRI markers predict subsequent lung health and development, independently and combined with echocardiogram, lung ultrasound, and traditional markers of BPD. The investigators anticipate that these new MRI markers will measure lung health safely and longitudinally in babies born extremely preterm. By identifying predictors of longer-term lung disease, clinicians will be able to allocate resources to babies at the highest risk of severe disease. Further, The investigators envision that MRI will help identify babies who would benefit most from interventions like stem cell therapy and be useful for evaluation of future treatments.