Characteristics of Avon Longitudinal Study of Parents and Children participants included in the analysis, by sex
| Females n=3909* | Males n=3717* | |
| n (%) | n (%) | |
| Non-white ethnicity | 75 (2.2) | 60 (1.8) |
| Maternal marital status | ||
| Never married | 527 (15.1) | 467 (13.7) |
| Widowed | <5 | 8 (0.2) |
| Divorced | 110 (3.2) | 118 (3.5) |
| Separated | 50 (1.4) | 36 (1.1) |
| 1st marriage | 2581 (73.9) | 2544 (74.8) |
| Marriage 2 or 3 | 224 (6.4) | 229 (6.7) |
| Household social class† | ||
| Professional | 517 (15.8) | 532 (16.7) |
| Managerial and technical | 1463 (44.6) | 1404 (44.1) |
| Non-manual | 793 (24.2) | 792 (24.9) |
| Manual | 343 (10.5) | 328 (10.3) |
| Part skilled and unskilled | 161 (4.9) | 128 (4.0) |
| Maternal education | ||
| Less than O level | 761 (22.2) | 724 (21.6) |
| O level | 1166 (34.1) | 1195 (35.7) |
| A level | 926 (27.1) | 883 (26.4) |
| Degree or above | 569 (16.6) | 548 (16.4) |
| Mother’s partner’s highest educational qualification | ||
| Less than O level | 965 (28.9) | 863 (26.5) |
| O level | 717 (21.5) | 724 (22.2) |
| A level | 916 (27.5) | 918 (28.2) |
| Degree or above | 737 (22.1) | 750 (23.0) |
| Maternal smoking during pregnancy | 660 (18.9) | 657 (19.2) |
| Mean (SD) | Mean (SD) | |
| Gestational age (weeks) | 39.6 (1.8) | 39.3 (1.9) |
| Birth weight (g) | 3370 (512) | 3469 (578) |
| Maternal age (years) | 28.8 (4.6) | 29.1 (4.7) |
| Maternal prepregnancy body mass index (kg/m2) | 22.8 (3.6) | 22.9 (3.8) |
*Note that denominators in this table do not sum exactly to N participants included in models due to some missing covariate data, which were not required for inclusion in our analyses.
†Household social class was measured as the highest of the mother’s or her partner’s occupational social class using data on job title and details of occupation collected about the mother and her partner from the mother’s questionnaire at 32 weeks’ gestation. Social class was derived using the standard occupational classification codes developed by the UK Office of Population Census and Surveys and classified as I, professional; II, managerial and technical; IIINM, non-manual; IIIM, manual; and IV&V, part skilled occupations and unskilled occupations.