Comparison of variables between 1st and 2nd born twin siblings
| Variable | Number of twin pairs | 2nd born twin only | 1st born twin only |
Odds ratio (95% CI) | p Value |
| Malpresentation | 283 | 101 | 17 | 5.9 (3.5 to 11) | <0.001 |
| SGA | 300 | 20 | 15 | 1.3 (0.7 to 2.8) | 0.5 |
| Intubation at resuscitation | 271 | 24 | 17 | 1.4 (0.7 to 2.8) | 0.4 |
| RDS | 271 | 41 | 15 | 2.7 (1.5 to 5.3) | <0.001 |
| Surfactant use | 296 | 53 | 16 | 3.3 (1.9 to 6.2) | <0.001 |
| Oxygen at 36 weeks | 288 | 22 | 25 | 0.9 (0.5 to 1.6) | 0.8 |
| IVH | 252 | 7 | 15 | 0.47 (0.2 to 1.2) | 0.1 |
| Mortality | 301 | 24 | 20 | 1.2 (0.6 to 2.3) | 0.7 |
SGA, Small for gestational age; RDS, respiratory distress syndrome; IVH, intraventricular haemorrhage.