Characteristics of the participants
| No headache N=5981 | Migraine N=1855 | Non-migrainous headache N=3358 | |
| Sex, female, % (n) | 48.9 (2924) | 77.0 (1429)** | 66.7 (2239)** |
| Age, mean years (SD) | 26.9 (0.07) | 28.1 (0.13)*** | 27.5 (0.10)*** |
| Foetal growth restriction, % (n) | 10.9 (653) | 13.2 (244)** | 12.3 (414)* |
| Caesarean section, % (n) | 3.6 (217) | 3.1 (58) | 2.7 (92)* |
Group mean or proportion is significantly different from no-headache control mean or proportion at *p<0.05, **p<0.01 and ***p<0.001 as determined by χ2 tests for categorical variables and independent t-tests for continuous variables.