Characteristics of the two epochs
| Cohorts | Epoch 1 (2003–2009) Lower oxygen limit (88–92%) | Epoch 2 (2010–2016) Higher oxygen limit (90–95% (99%)) | P value |
| Number (n) | 307 | 344 | |
| Gestation (SD) (weeks) | 29.1 (2) | 29.3 (2) | 0.24 |
| Birth weight (SD) (g) | 1116 (309) | 1167 (338) | 0.05 |
| Mortality (%) | 13/294 (4) | 0/344 (0) | 0.0001 |
| Sepsis (including NEC) | 237/302 (78%) | 131/318 (41%) | <0.0001 |
| Intraventricular haemorrhage | 61/302 (20%) | 140/320 (44%) | 0.0001 |
| ROP cases detected | 94/307 (31%) | 94/320 (29%) | 0.73 |
| ROP progression | 15/307 (5%) | 34/314 (11%) | 0.006 |
| ROP cases requiring treatment | 44/307 (14%) | 19/320 (6%) | 0.0005 |
| APROP cases | 3/304 (1%) | 3/317 (1%) | 0.96 |
| Surfactant administered | 139/301 (46%) | 186/319 (58%) | 0.0025 |
| Steroid administered | 244/302 (81%) | 234/314 (75%) | 0.06 |
| Maternal PE | 72/302 (24%) | 77/315 (24%) | 0.86 |
| IPPV | |||
| Not ventilated <7 days 7 days or more | 84/307 (27%) 98/307 (32%) 125/307 (41%) | 138/344 (40%) 124/344 (36%) 82/344 (24%) | <0.0001 |
| Transfusion | 178/302 (59%) | 139/321 (43%) | <0.0001 |
| Heart disease | 158/302 (52%) | 121/320 (40%) | 0.0003 |
APROP, aggressive posterior retinopathy of prematurity; IPPV, invasive positive pressure ventilation; NEC, necrotising enterocolitis; PE, pre-eclampsia; ROP, retinopathy of prematurity.