Table 1

List of potential confounders included in the adjusted models

Potential confounderLevels
*Reference category.
†Subscale of the Crown-Crisp experiential index (CCEI) relating to free floating anxiety.
‡Maximum level of exposure reported by the mother in the questionnaires completed at 8 weeks, 18–20 weeks and/or 32 weeks gestation.
Child’s sexFemale*, male
Mother’s education levelBelow O level, O level only*, A level or higher, unknown
Mother’s housing tenureOwned/mortgaged*, council rented, non-council rented, unknown/other
Mother’s ethnic originWhite*, non-white, unknown
Mother’s parity0*, 1, 2+, unknown
Mother’s age (years)<20, 20–24, 25–29*, 30–34, 35+
Birth seasonJanuary–March, April–June, July–September, October–December*
Breast feeding in first 6 monthsNo, yes*, unknown
Day care use in first 8 monthsNo*, yes, unknown
Antibiotic use in first 6 monthsNever*, once, more than once, unknown
Mother’s anxiety score in pregnancy (CCEI units)†0–4*, 5–9, 10+, unknown
Pets kept in first yearNo pets*, cat and/or dog, other pets only, unknown
Maternal smoking in pregnancy (cigarettes/day)‡Not exposed*, passive only, 1–9/day, 10–19/day, 20+/day, unknown
Weekend tobacco exposure in first 6 monthsNot exposed*, exposed, unknown
Mother’s body mass index (BMI) (kg/m2)<20, 20–24.99*, 25–29.99, 30+, unknown
Crowding in home (persons/room)Up to 1*, 1+, unknown
Damp and/or mould in homeNo*, yes, unknown
Child’s birthweight (g)<2500, 2500–2999, 3000–3499*, 3500–3999, 4000+, unknown
Child’s gestational age at birth (weeks)<37, 37–40*, 41+
Multiple pregnancyNo*, yes
Child’s head circumference (cm)<33, 33–34.99*, 35–36.99, 37+, unknown
Child’s birth length (cm)<48, 48–50.99*, 51–53.99, 54+, unknown
Mother ever had asthmaNo*, yes
Mother ever had eczemaNo*, yes
Mother ever had rhinitisNo*, yes
Mother ever had migraineNo*, yes
Mother’s atopic/migraine history unknownNo*, yes
Mother had cold/flu in late gestationNo*, yes
Mother had urinary infection in late gestationNo*, yes
Mother had other infections in late gestationNo*, yes
Mother’s history of infections unknownNo*, yes