Description of characteristics of study population
| Month of birth | ||||
| All infants |
January 2010–July 2012
(period 1; pre-CG149) | August 2012–March 2021 (period 2) |
April 2021–December 2022
(period 3; post-NG195) | |
| Number of infants | 84 626 | 16 391 | 57 426 | 10 809 |
| Births per month, median (IQR) | 546 (517, 569) | 536 (504, 560) | 557 (535, 581) | 512 (497, 543) |
| Gestational age in weeks, median (IQR) | 29 (27, 31) | 29 (27, 31) | 29 (27, 31) | 29 (27, 31) |
| Birth weight in grams, median (IQR) | 1240 (960, 1515) | 1246 (977, 1520) | 1240 (960, 1511) | 1232 (950, 1510) |
| Birth weight z-score, median (IQR) | 0.03 (−0.62, 0.60) | 0.05 (−0.60, 0.61) | 0.02 (−0.62, 0.59) | 0.03 (−0.66, 0.61) |
| Female sex, n (%) | 38 858 (45.9) | 7583 (46.3) | 26 370 (45.9) | 4905 (45.4) |
| Neonatal intensive care unit | 44 586 (52.7) | 8147 (49.7) | 30 612 (53.3) | 5827 (53.9) |
| Local neonatal unit | 32 606 (38.5) | 6707 (40.9) | 21 873 (38.1) | 4026 (37.3) |
| Special care baby unit | 6531 (7.7) | 1364 (8.3) | 4340 (7.6) | 827 (7.7) |
| Missing | 903 (1.07) | 173 (1.1) | 601 (1.1) | 129 (1.2) |
| Length of hospital stay in days, median (IQR) | 53 (38, 78) | 52 (37, 77) | 53 (38, 78) | 54 (38, 80) |
CG149, clinical guideline 149; NG195, NICE guideline 195.