Table 2.
Background characteristics after propensity score matching of extremely preterm infants (<28 gestational weeks) born in England in 2008 to 2015, by hospital of birth and transfer status at 48 hours of age. Values are numbers (percentages) unless stated otherwise
| Characteristics | Controls (n=727) | Upward transfer (n=727) | Standardised difference (matched)* | Non-tertiary care (n=727) | Standardised difference (matched)† | Standardised difference (matched)‡ |
|---|---|---|---|---|---|---|
| Median (interquartile range) gestational weeks | 26.0 (25.0-27.0) | 26.0 (25.0-27.0) | 0.000 | 26.0 (25.0-27.0) | 0.000 | 0.000 |
| Mean (SD) birth weight (g) | 900 (56) | 900 (69) | −0.012 | 888 (65) | 0.015 | 0.027 |
| Mean (SD) birth weight z score | 0.099 (0.24) | 0.103 (0.26) | −0.024 | 0.099 (0.25) | 0.030 | 0.054 |
| Boys | 298 (41.0) | 298 (41.0) | 0.000 | 298 (41.0) | 0.000 | 0.000 |
| Multiple birth | 158 (21.7) | 162 (22.3) | −0.009 | 172 (23.7) | −0.033 | −0.024 |
| Missing | 0 | 0 | 1 | |||
| Smoking in pregnancy | 129 (20.1) | 157 (24.1) | −0.068 | 146 (23.4) | −0.056 | 0.012 |
| Missing | 86 (11.8) | 76 (10.5) | 103 (14.2) | |||
| Caesarean delivery | 416 (57.2) | 405 (55.7) | 0.010 | 398 (54.7) | 0.046 | 0.036 |
| Missing | 0 | 0 | 0 | |||
| Surfactant during resuscitation | 701 (97.9) | 695 (98.0) | −0.006 | 683 (95.9) | 0.022 | 0.025 |
| Missing | 11 (1.5) | 18 (2.5) | 15 (2.1) | |||
| Antenatal steroids | 565 (80.5) | 565 (78.9) | 0.000 | 565 (81.2) | 0.000 | 0.000 |
| Missing | 25 (3.4) | 11 (1.5) | 31 (4.3) | |||
| Apgar score <3 at 1 min | 144 (21.7) | 144 (21.8) | −0.014 | 139 (20.9) | −0.016 | −0.017 |
| Missing | 64 (8.8) | 67 (9.2) | 62 (8.5) | |||
| Apgar score <3 at 5 min | 34 (5.3) | 34 (5.3) | −0.050 | 25 (3.8) | −0.049 | 0.005 |
| Missing | 84 (11.6) | 82 (11.3) | 74 (10.2) |
Upward transfer=infants born in hospitals with local neonatal units and transferred to tertiary hospitals within 48 hours of birth; non-tertiary care=infants born in hospitals with local neonatal units and not transferred within 48 hours of birth; control=infants born in tertiary hospitals and not transferred within 48 hours of birth.
*
Controls versus upward transfer group.
†
Controls versus non-tertiary care group.
‡
Upward transfer group versus non-tertiary care group.