Key background characteristics
| Entire cohort | Matched cohort | |||
| Early PN (n=43 436) | Late PN (n=21 597) | Early PN (n=8147) | Late PN (n=8147) | |
| Infant characteristics at birth | ||||
| Gestational age (weeks), mean (SD) | 27.7 (2.0) | 28.9 (2.0) | 28.5 (2.0) | 28.5 (2.0) |
| Birth weight (kg), mean (SD) | 1.02 (0.303) | 1.22 (0.342) | 1.14 (0.322) | 1.15 (0.32) |
| Birth weight z-score, mean (SD) | −0.08 (0.99) | 0.16 (0.93) | 0.06 (0.96) | 0.06 (0.93) |
| Girls, n (%) | 19 880 (46.3) | 9385 (44.8) | 3633 (45.7) | 3633 (45.7) |
| Maternal factors | ||||
| Maternal age, mean (SD) | 30.5 (6.3) | 30.1 (6.3) | 30.3 (6.4) | 30.3 (6.3) |
| Maternal diabetes, n (%) | 624 (1.4) | 249 (1.2) | 108 (1.3) | 102 (1.3) |
| Maternal gestational diabetes, n (%) | 1172 (2.7) | 678 (3.1) | 489 (3.0) | 496 (3.0) |
| Maternal gestational hypertension, n (%) | 3167 (7.3) | 1759 (8.1) | 692 (8.5) | 704 (8.6) |
| Maternal pre-eclampsia, n (%) | 1973 (4.5) | 529 (2.5) | 232 (2.8) | 242 (3.0) |
| Prolonged rupture of membranes, n (%) | 4715 (10.9) | 2633 (12.2) | 957 (11.8) | 946 (11.6) |
| Chorioamnionitis, n (%) | 3019 (8.3) | 1200 (7.2) | 478 (7.3) | 472 (7.3) |
| Complete course of antenatal steroids, n (%) | 29 786 (71.9) | 13 736 (68.9) | 5268 (69.2) | 5256 (69.2) |
| Infant factors after birth | ||||
| Apgar score <5 at 5 min, n (%) | 5186 (13.5) | 1837 (9.6) | 813 (11.2) | 794 (11.0) |
| Intubation during resuscitation, n (%) | 26 752 (62.0) | 9445 (43.7) | 4158 (51.4) | 4144 (50.9) |
| Infant factors on first day | ||||
| Ventilated on first day, n (%) | 33 506 (77.1) | 12 728 (58.9) | 5460 (67.0) | 5463 (67.0) |
| Surfactant given, n (%) | 21 384 (49.2) | 8882 (41.1) | 3739 (46.0) | 3740 (46.0) |
| Inotropes on first day, n (%) | 9544 (22.0) | 3352 (15.5) | 1512 (19.4) | 1495 (18.4) |
| Treated for infection on first day, n (%) | 25 428 (58.5) | 12 323 (57.6) | 4767 (58.5) | 4762 (58.8) |
| Organisational factors | ||||
| Born in level 3 unit (NICU), n (%) | 26 790 (61.7) | 10 037 (46.5) | 4043 (49.7) | 4060 (49.9) |
| Transferred on first day, n (%) | 6205 (14.3) | 2907 (13.5) | 1203 (14.8) | 1200 (14.7) |
NICU, neonatal intensive care unit; PN, parenteral nutrition.