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Background and objectives: Follow-up studies of children and young adults born very-to-moderately preterm show persistent and significant lung function deficits. The aim of the study was to determine lung function and airway mechanics in school-aged children born in 2004 to 2007 and extremely preterm (after 22-26 weeks of gestation).

Methods: In a population-based cohort of children born extremely preterm and controls born at term (n=350), follow-up at 61/2-years-of-age was performed using spirometry and impulse oscillometry. Associations to gestational age, smallness for gestational age (SGA), and bronchopulmonary dysplasia (BPD) were assessed.

Results: Children born extremely preterm had lower forced vital capacity (FVC, z-score: -0.7, 95%CI: -1.0;-0.4), forced expiratory volume (FEV1, z-score: -1.1, 95%CI: -1.4; -0.8), higher frequency-dependence of resistance (R5-20, 0.09, 95%CI: 0.05; 0.12 kPaL(-1)s(-1)) and larger area under the reactance curve (AX, 0.78, 95%CI: 0.49; 1.07kPaL(-1)) than controls. In children born at 22-24 weeks of gestation, 24% had FVC and 44% had FEV1 below the lower limit of normal. SGA and severe BPD only marginally contributed to pulmonary outcomes. Asthma-like disease was reported in 40% of extremely preterm children and 15% of controls.

Conclusion: Many children born extremely preterm have altered airway mechanics and significant obstructive reduction in lung function. This warrants consideration for treatment and continued follow-up.