Demographics and clinical characteristics
| No BPD | Grade 1 BPD | Grade 2 BPD | Grade 3 BPD | Death prior to 36 weeks | P value* | |
| N | 3257 | 2795 | 1526 | 551 | 1052 | |
| Birth weight, g, mean±SD | 951±173 | 838±176 | 778±173 | 752±168 | 722±161 | <0.0001 |
| Gestational age, weeks, mean±SD | 26.7±1.24 | 25.8±1.49 | 25.5±1.51 | 25.1±1.52 | 24.7±1.49 | <0.0001 |
| Male, n (%) | 1480 (45) | 1420 (51) | 896 (59) | 315 (57) | 613 (58) | <0.0001 |
| Race | ||||||
| Black, n (%) | 1576 (50) | 973 (36) | 511 (35) | 237 (44) | 415 (41) | |
| White, n (%) | 1399 (44) | 1531 (57) | 870 (59) | 267 (50) | 533 (52) | |
| Other, n (%) | 198 (6) | 196 (7) | 100 (7) | 32 (6) | 73 (7) | <0.0001 |
| Hispanic ethnicity, n (%) | 447 (14) | 439 (16) | 228 (15) | 48 (9) | 142 (14) | 0.0004 |
| Patent ductus arteriosus, n (%) | 971 (30) | 1445 (52) | 950 (62) | 356 (65) | 419 (40) | <0.0001 |
| Sepsis, n (%) | 378 (12) | 624 (22) | 444 (29) | 253 (46) | 339 (41) | <0.0001 |
| Surgical necrotising enterocolitis, n (%) | 46 (1) | 61 (2) | 51 (3) | 63 (11) | 156 (15) | <0.0001 |
| Antenatal corticosteroids, n (%) | 2990 (92) | 2543 (91) | 1379 (90) | 515 (93) | 904 (86) | <0.0001 |
BPD, bronchopulmonary dysplasia.