Maternal characteristics of study cohort in North East England
| Variable | Categories | Total in cohort (%) | Smoking status: | ||
| Non-Smokers | Smokers | Missing | |||
| Maternal age (years) | 15–20 | 3501 (9.3) | 1858 (6.9) | 1626 (15.3) | 17 (20.7) |
| 21–30 | 20 401 (54.1) | 14 135 (52.3) | 6226 (58.8) | 40 (48.8) | |
| 31–40 | 13 163 (34.9) | 10 538 (39.0) | 2600 (24.5) | 25 (30.5) | |
| 41+ | 651 (1.7) | 510 (1.9) | 141 (1.3) | 0 (0.0) | |
| Missing | 10 (0.0) | 9 (0.0) | 1 (0.0) | 0 (0.0) | |
| Parity | First child | 13 476 (35.7) | 10 449 (38.6) | 3000 (28.3) | 27 (32.9) |
| Second child | 11 166 (29.6) | 8205 (30.3) | 2942 (27.8) | 19 (23.2) | |
| Third + child | 7362 (19.5) | 4540 (16.8) | 2796 (26.4) | 26 (31.7) | |
| Missing | 5722 (15.2) | 3856 (14.3) | 1856 (17.5) | 10 (12.2) | |
| BMI (kg/m2) | Underweight (<20) | 747 (2.0) | 440 (1.6) | 304 (2.9) | 3 (3.7) |
| Healthy (20–24.9) | 12 026 (31.9) | 8603 (31.8) | 3389 (32.0) | 34 (41.5) | |
| Overweight (25–29.9) | 6985 (18.5) | 4976 (18.4) | 1990 (18.8) | 19 (23.2) | |
| Obese (30+) | 5725 (15.2) | 3964 (14.7) | 1752 (16.5) | 9 (11.0) | |
| Missing | 12 243 (32.5) | 9067 (33.5) | 3159 (29.8) | 17 (20.7) | |
| Ethnic group | White | 33 614 (89.1) | 23 491 (86.8) | 10 041 (94.8) | 82 (100.0) |
| Caucasian | 2736 (7.3) | 2512 (9.3) | 224 (2.1) | 0 | |
| Missing | 1376 (3.6) | 1047 (3.9) | 329 (3.1) | 0 | |
| SEP (categories defined by fifths of IMD score) | Least deprived (0–16) | 8380 (22.2) | 7142 (26.4) | 1231 (11.6) | 7 (8.5) |
| Middle three-fifths (17–64) | 27 012 (71.6) | 18 408 (68.1) | 8536 (80.6) | 68 (82.9) | |
| Most deprived (65–80) | 1674 (4.4) | 971 (3.6) | 698 (6.6) | 5 (6.1) | |
| Missing | 660 (1.7) | 529 (2.0) | 129 (1.2) | 2 (2.4) | |
| Total | 37 726 | 27 050 | 10 594 | 82 | |
BMI, body mass index; SEP, socioeconomic position (categories defined by fifths of Index of Multiple Deprivation (IMD) score).