Background As a result of advances in perinatal care, more small preterm infants survive. There are concerns that preterm birth and its treatments may harm pulmonary development and thereby lead to chronic airway obstruction in adulthood.

Objective To assess the development of spirometric lung function variables from mid-childhood to adulthood after extreme preterm birth.

Methods Two population-based cohorts born at gestational age ≤28 weeks or with birth weight ≤1000 g performed lung function tests at 10 and 18 and at 18 and 25 years of age, respectively, together with matched term-born controls. The results are presented as z scores, normalised for age, sex and height. Longitudinal development was compared for groups born at term and preterm, split by a history of absence (n=20), mild (n=38) or moderate/severe (n=25) neonatal bronchopulmonary dysplasia (BPD).

Results The preterm-born cohorts, particularly those with neonatal BPD, had significantly lower forced expiratory volume in 1 s and mid-expiratory flow than those born at term at all assessments (z scores in the range −0.40 to −1.84). Within each of the subgroups the mean z scores obtained over the study period were largely similar, coefficients of determination ranging from 0.64 to 0.82. The pattern of development for the BPD subgroups did not differ from each other or from the groups born at term (tests of interaction).

Conclusions Airway obstruction was present from mid-childhood to adulthood after extreme preterm birth, most evident after neonatal BPD. Lung function indices were tracking similarly in the preterm and term-born groups.