Cystic Fibrosis (CF) is an inherited disease multi-organ disease that predominately affects the lungs. A key feature of the disease is progressive lung disease, and the main cause of death is respiratory failure. Preservation of good lung function through childhood is a major goal of treatment. Research has shown that somatic growth, as indicated by weight and height, in early life is associated with later lung function, but much of this research has not made full use of the longitudinal data available in CF patient registries.

This thesis aimed to extend current understanding of early growth in CF using data from the UK and Canadian CF Registries. The first two aims were to model trajectories of early growth and link summaries of growth to later lung function. The third was to investigate the extent to which weight trajectory mediated the effect of early disease status on first lung function test. The last aim was to assess the effectiveness of treatment to improve weight.

On average children tracked in terms of weight between 1 and 5 years. A greater weight at 1 year, as well as increasing weight over time, was associated with better first lung function test at approximately age 6 years. Expanding these analyses using mediation analysis, weight only partially mediated the association between disease severity at diagnosis and first lung function test. The use of oral supplemental feeding to improve weight was not associated with improved lung function or weight at approximately age 6.

The results are consistent with better weight having beneficial effect on lung function, but that is not to say that increasing weight through any means would have the same effect.