A prospective study was conducted in the Neonatal Intensive Care Unit of the University Children's hospital between September 1, 2008 and November 30, 2010. The entry criteria were (1) preterm birth below 32 weeks gestational age, (2) birthweight<1500g (VLBW). During the follow-up period, bronchopulmonary dysplasia (BPD) was diagnosed in 68 (61%) infants, including 40 (36%) children with mild disease, 13 (12%) with moderate and 15 (13%) with severe BPD. Forty-three babies served as a control group (no BPD).

One hundred twenty newborns were included at the start of the study. Three blood samples (0.3 ml) were drawn from all the study participants for microarray assessment of gene expression profiles around the 5th, 14th and 28th days of life. Note that microarrays were not taken for all patients at all time points (A,B,C).