The moderate-to-severe BPD group exhibited higher levels of CO-Hb compared with the no-or-mild BPD group between postnatal days 5 and 8 (median [range]: 1.1% [0.9–1.8%] versus 0.8% [0.6–1.4%], p < 0.01), 12 and 15 (median [range]: 0.6% [0.6–1.8%] versus 0.4% [0.0–0.7%], p < 0.05), and 19 and 22 (median [range]: 0.5% [0.3–0.9%] versus 0.3% [0.0–0.6%], p < 0.01). Here, GSTM1 is linked to bronchopulmonary dysplasia.