Risk of asthma in the lower birthweight twin relative to the higher birthweight twin in a sample of Danish twin pairs, 3–9 years of age
| Birth weight difference (g) | All twin pairs | MZ twin pairs | DZ twin pairs | ORMZ=ORDZ | |||
| OR (95% CI) | p Value | OR (95% CI) | p Value | OR (95% CI) | p Value | p Value* | |
| Any difference† | 1.31 (1.03 to 1.65) | 0.027 | 1.33 (0.72 to 2.46) | 0.356 | 1.29 (1.08 to 1.54) | 0.005 | 0.935 |
| ≥100 | 1.26 (1.05 to 1.57) | 0.015 | 1.75 (0.86 to 3.56) | 0.122 | 1.23 (1.01 to 1.49) | 0.042 | 0.516 |
| ≥200 | 1.29 (1.04 to 1.60) | 0.019 | 1.71 (0.68 to 4.35) | 0.257 | 1.28 (1.02 to 1.61) | 0.030 | 0.661 |
| ≥300 | 1.40 (1.09 to 1.81) | 0.008 | 3.33 (0.92 to 12.11) | 0.067 | 1.37 (1.05 to 1.77) | 0.019 | 0.413 |
| ≥400 | 1.21 (0.91 to 1.81) | 0.192 | 2.33 (0.60 to 9.02) | 0.220 | 1.21 (0.90 to 1.63) | 0.202 | 0.524 |
| ≥500 | 1.20 (0.84 to 1.71) | 0.322 | 2.50 (0.49 to 12.89) | 0.273 | 1.17 (0.81 to 1.69) | 0.402 | 0.538 |