Ventilation in preterm infants and lung function at 8 years

To the Editor: Doyle et al. (July 27 issue)1 found no reduction in the rate of bronchopulmonary dysplasia and an increased rate of obstructive lung disease in a cohort of infants born in 2005, as compared with a cohort born in 1997. The lower survival rate that was observed and the shorter courses of mechanical ventilation in 1991 and 1992, as compared with the later cohorts (1997 and 2005), suggest that babies who were at the highest risk for bronchopulmonary dysplasia did not survive long enough for it to develop; thus, the earlier cohort (1991–1992) cannot be compared with the . . .