INTRODUCTION
Preterm birth, defined as birth at less than thirty-seven weeks
gestation, is the leading cause of mortality in children under five
years of age and an important cause of morbidity, associated with
prolonged hospitalizations and multisystem complications that persist
throughout childhood and into adulthood1. Rates of
preterm birth have increased globally over the past twenty years and
currently preterm births account for more than 11% of
livebirths2-3. Bronchopulmonary dysplasia (BPD) is a
major complication of preterm birth and the most common cause of chronic
lung disease in infancy. Based on the 2001 National Heart, Lung, and
Blood Institute (NHLBI) definition4, it is estimated
that up to 50,000 infants develop BPD each year in the United
States5-6. While advances in neonatal care and
technology, such as gentler ventilation strategies, exogenous
surfactant, and the widespread use of postnatal steroids, have led to
improved survival and outcomes for these infants, the incidence of BPD,
which is defined as the need for supplemental oxygen for at least
twenty-eight days after birth, has remained
unchanged6.
Several previous studies, including a meta-analysis by Kotecha et
al. 7, have shown that preterm patients, and
especially those with BPD, display significant lung function impairment
later in life compared to their term peers. These individuals are at an
increased risk of respiratory morbidity later in childhood, with
increased respiratory symptoms, structural abnormalities, and decreased
lung function, primarily characterized by airway obstruction, altered
peripheral lung mechanics, and hyperinflation8. A
study of two hundred preterm children in Australia, including 126 with
BPD and 74 without BPD, demonstrated that lung function trajectories in
survivors of preterm birth are impaired and those with BPD, ongoing
respiratory symptoms, or findings on chest computed tomography (CT) have
the poorest trajectories, and are at the greatest risk of developing
significant lung disease in adulthood8. Similar
results were appreciated in a longitudinal observational study of the
EPICure cohort9, a cohort of extremely low birth
weight infants which showed that individuals displayed impaired lung
function and increased respiratory morbidity that persisted into middle
childhood, defined as eleven years of age, with findings especially
notable in infants with BPD. Interestingly, this impairment was
appreciated in infants born in both the pre-surfactant era as well as
the modern era during which new management techniques have been
employed10-11. These findings all suggest that
long-term follow-up is especially important in this population given the
concern for chronic obstructive pulmonary disease during adult life.
This population has remained steady and even grown in size in the past
several years12, and as a result, the global burden of
lung disease following preterm birth is set to rise which has
significant implications for adult providers and the health care system
as a whole.
Overall, however, little is known about the potential modifiable
predictors of lung function in this population specifically during the
first two years of life, a period of postnatal life in which alveolar
growth occurs most rapidly13. One retrospective study
of 322 preterm infants with BPD showed that the initial severity of an
individual’s BPD was an important predictor of pulmonary function
abnormalities (at eight years old and then subsequently at fifteen years
old) as well as health care usage during childhood14.
The aim of this study was to investigate demographic and clinical
characteristics as well as growth measurements at birth and at two years
of age to determine what factors are most strongly predictive of lung
function at six years of age. We hypothesized that in the outpatient
setting, socioeconomic factors, growth parameters, and need for
respiratory support would influence lung function at 6 years of age in
children with a history of bronchopulmonary dysplasia.