| Variable | Cases (n = 322) | Controls (n = 934) | p |
| Maternal age, years, % | |||
| ⩽20 | 4.0 | 4.1 | |
| 21–35 | 81.4 | 85.3 | |
| >35 | 14.6 | 10.6 | 0.154 |
| Maternal education, % | |||
| ⩽ Primary school | 20.5 | 23.2 | |
| Secondary | 71.7 | 66.0 | |
| University | 7.8 | 10.8 | 0.122 |
| Primigravidae, % | 48.5 | 45.5 | 0.361 |
| Smoking in pregnancy, % | |||
| No | 56.5 | 67.0 | |
| 1–10 cigarettes/day | 33.5 | 27.6 | |
| >10 cigarettes/day | 10.0 | 5.4 | <0.001 |
| Body mass index (SEM), kg/m2 | 23.2 (0.2) | 23.7 (0.1) | 0.031 |
| Weight gain per week during pregnancy (SEM), g | 255 (6) | 296 (3) | <0.001 |
| Weight of infant (SEM), g | 2041 (25) | 3340 (14) | <0.001 |
| Gestational age (SEM), days | 250 (1) | 277 (1) | <0.001 |