Descriptive characteristics of individuals included in analyses (n=5011)*
| Prefactor or postfactor | Details of measurement in 1970 | Coding framework for analysis |
| 1. Parental occupational class | Father’s occupation at birth using the Registrar General’s 1966 Classification of Occupation; if missing, maternal occupational class was used. | Categorical (I—professional or II—managerial/technical; III—manual or non-manual; IV—partly skilled or V-unskilled) |
| Prenatal maternal factors | ||
| 2. Maternal age at birth | Calculated using the mother and child’s dates of birth. | Continuous (years) |
| 3. Previous pregnancies | Calculated from detailed reporting of all previous pregnancies at the time of the cohort members’ birth, including miscarriages and ectopic pregnancies. | Categorical (0, 1–2, 3+) |
| 4. Smoking during pregnancy | Reported yes or no to midwife interview. | Categorical (yes/no) |
| 5. Clinical diabetes | Reported by midwives at birth.* Due to potential under-reporting of diabetes at birth, this factor was supplemented with additional data collected at age 5, where a health visitor examined all home visit records, consultation record cards, family records, child health clinics and child welfare clinic records and reported if diabetes was noted as a risk factor during the perinatal period (pregnancy, labour or postnatal in first week). Note that details (eg, type 1, type 2, gestational, etc) were not collected. | Categorical (yes/no) |
| Postnatal infant factors | ||
| 6. Gestational age | Calculated from the reported first day of the last menstrual period to birth. The data processing team in 1970 coded ‘implausible’ values (after consideration of date of last delivery, duration of gestation, birth weight) as missing. | Categorical (preterm <37 weeks; term 37–41 weeks; post-term >41 weeks) |
| 7. Birth weight | Recorded in pounds or grams. | Continuous (kg) |
| 8. Breast feeding | At the age 5 home visit, mothers were asked if, and for how long, the study member was partly or wholly breast fed. | Categorical (0–3 months; 3+ months) |
| 9. Infant health concerns | At birth, nurses recorded if the baby had any of the following binary health indicators or interventions: jaundice, breathing difficulties including respiratory distress syndrome, cyanotic attacks, fits or convulsions, cerebral signs, fractures, cephalhaematoma, sticky eyes, discharge form umbilicus, received exchange transfusions, underwent an operation or had any other illness/condition. | Categorical (0, 1, 2+) |
*Question: ‘Has the mother clinical diabetes?’