Introduction: Clinical labels, such as bronchopulmonary dysplasia (BPD), assigned in the neonatal ICU are imperfect predictors of reduced peak lung function or early-onset adult respiratory disease. We aimed to define potential lung function trajectories (i.e. persistently low or declining) and establish which early life factors are associated with specific trajectories for those born preterm

Methods: 200 very preterm (?32 weeks gestation), 126 with BPD and 67 term-born participants attended 629 research visits between age 4 and 23 years. Trajectories for FEV₁/FVC z-scores (as a marker of airway obstruction) were modelled using group-based trajectory modelling, via ?traj? plugin (STATA, v16.0). Multivariate analyses determined risks associated with belonging to a poorer trajectory.

Results: Two FEV₁/FVC z-score trajectories emerged from 169 preterm participants with acceptable measures from two or more visits. These trajectories were labelled ?preserved? (quadratic trend; 45.1% of cohort) and ?low declining? (linear trend, 54.9% of cohort). Significant risk factors for belonging to the ?low declining? FEV₁/FVC trajectory compared to the ?preserved? trajectory included respiratory admission ever (Odds Ratio (OR) 4.33; 95% CI 1.54, 12.14, p=0.006), smoking in the family (OR 2.39; 95% CI 1.27, 10.96, p=0.017) and worse CT total score (OR 1.14; 95% CI 1.03, 1.27, p=0.011).

Conclusion: We have demonstrated two distinct lung function trajectories for those born preterm. Exposure to tobacco smoke, a respiratory infection and abnormalities on CT are associated with a poorer trajectory.