Introduction
Long-term pulmonary outcome in preterm infants usually involve chronic respiratory impairment such as airway obstruction(1)and low diffusion capacity(2). Perinatal inflammation, fetal growth restriction, bronchopulmonary dysplasia (BPD) and gender are risk factors affecting the immature lung during the first years of life(3-5). There is evidence that persistence of respiratory symptoms, lung function impairment and abnormalities of the lung structure may persist into adulthood(6, 7). Infants with BPD have low respiratory compliance in the first month of life, but with some normalization at 2 years of age(8). Up to 8 years of age, there is still a reduction of forced flows and volumes in these children(4, 9). In an 11-year follow-up of extremely preterm infants, the children had reduced forced expiratory volume in 1 second (FEV1) and forced expiratory flow between 25-75% (FEF25-75) compared to term born classmates(10). It has been suggested that the observed increase in airway obstruction could be an expression of early impaired airway development during childhood, whereas there seem to be some catch-up through early life(7, 11). Furthermore, small airway abnormalities, could be a risk for future chronic lung disease and further decrease the respiratory outcome after preterm birth(12), since prematurity per se is also a well-known risk factor. A reduced lung function already at childhood, may lead to a lower lung function throughout life(13).
Since BPD is a poor predictor of prematurity-associated lung disease(11), and the respiratory outcomes after preterm birth seem to be more dependent on the prematurity per se, it is important to investigate preterm-born children also beyond BPD.(14)
The primary aim of the study was to extensively investigate lung function pattern at 12 years of age in children born very preterm, with or without BPD during infancy as compared to term born controls. The secondary aim was to study how different neonatal comorbidities and sex may affect lung function and prevalence of airway symptoms during childhood in preterm children.