| Cases (n = 5124) | Controls (n = 30053) | Unadjusted OR(95% CI) | |
| n (%)* | n (%)* | ||
| Median (IQR) maternal age at delivery (years) | 29.6 (25.5–33.2) | 29.4 (25.5–33.1) | 1.01 (1.00 to 1.01) |
| Maternal body mass index (kg/m2) | |||
| Underweight (<18.5) | 163 (3.2) | 827 (2.8) | 1.19 (1.00 to 1.42) |
| Normal (18.5–24.9) | 2031 (39.6) | 12280 (40.9) | Reference |
| Overweight (25–29.9) | 709 (13.8) | 4131 (13.7) | 1.04 (0.95 to 1.14) |
| Obese (⩾30) | 385 (7.5) | 1997 (6.6) | 1.16 (1.03 to 1.31) |
| Missing | 1836 (35.8) | 10818 (36.0) | 1.01 (0.93 to 1.10) |
| Maternal smoking status | |||
| Non-smoker | 2590 (50.5) | 15046 (50.1) | Reference |
| Ex-smoker | 269 (5.2) | 1473 (4.9) | 1.06 (0.92 to 1.22) |
| Current smoker | 1136 (22.2) | 6637 (22.1) | 1.00 (0.92 to 1.08) |
| Missing | 1129 (22.0) | 6897 (23.0) | 0.92 (0.84 to 1.01) |
| Household Townsend score quintile | |||
| 1 (least deprivation) | 826 (16.1) | 4976 (16.6) | Reference |
| 2 | 592 (11.6) | 3499 (11.6) | 1.02 (0.90 to 1.15) |
| 3 | 586 (11.4) | 3387 (11.3) | 1.05 (0.93 to 1.19) |
| 4 | 506 (9.9) | 2833 (9.4) | 1.08 (0.95 to 1.24) |
| 5 (most deprivation) | 400 (7.8) | 2337 (7.8) | 1.04 (0.90 to 1.21) |
| Missing | 2214 (43.2) | 13021 (43.3) | 0.87 (0.67 to 1.12) |
| Term of pregnancy | |||
| Preterm | 366 (7.1) | 858 (2.9) | 2.62 (2.21 to 3.11) |
| Term | 705 (13.8) | 4503 (15.0) | Reference |
| Post-term | 8 (<0.5) | 39 (<0.5) | 1.29 (0.54 to 3.05) |
| Missing | 4045 (78.9) | 24653 (82.1) | 1.01 (0.88 to 1.16) |
| Sex of child | |||
| Female | 2172 (42.4) | 14829 (49.4) | Reference |
| Male | 2952 (57.6) | 15224 (50.7) | 1.32 (1.25 to 1.40) |
| Singleton or multiple delivery | |||
| Singleton | 4996 (97.5) | 29655 (98.7) | Matching variable |
| Twin | 128 (2.5) | 398 (1.3) | |
| Year of birth | |||
| 1988–9 | 196 (3.8) | 1104 (3.7) | Matching variable |
| 1990–4 | 1567 (30.6) | 9192 (30.6) | |
| 1995–9 | 1768 (34.5) | 10389 (34.6) | |
| 2000–4 | 1593 (31.1) | 9368 (31.2) |
*Proportion of cases or controls. IQR, interquartile range.