Gestation (weeks) | Number of twin pairs |
2nd born twin only |
1st born twin only |
Odds ratio (95% CI) | p Value |
A | |||||
23–25 | 37 | 3 | 3 | 1.0 (0.13 to 7.5) | 1.0 |
26–27 | 56 | 5 | 3 | 1.7 (0.32 to 11) | 0.7 |
28–29 | 60 | 11 | 4 | 2.8 (0.82 to 12) | 0.1 |
30–31 | 118 | 22 | 5 | 4.4 (1.6 to 15) | 0.002 |
B | |||||
23–25 | 39 | 6 | 3 | 2 (0.43 to 12) | 0.5 |
26–27 | 60 | 8 | 3 | 2.7 (0.64 to 16) | 0.2 |
28–29 | 66 | 14 | 3 | 4.7 (1.3 to 25) | 0.01 |
30–31 | 131 | 25 | 7 | 3.6 (1.5 to 9.8) | 0.002 |