Table 2 Confounders and covariates (n = 7,410)

Confounders

Mean (SD)

Range

Maternal age at childbirth (years)

29.1 (1.23)

15–44

N

%

Maternal education

  (≥ A’ levels)

3068

41.3

  (< A’ levels)

4111

55.5

  Missing

231

3.2

Deprivation index

  Highest quintile

1965

26.5

  60–80%

1162

15.7

  40–60%

1054

14.2

  20–40%

885

11.9

  Lowest quintile

765

10.3

  Missing

1579

21.3

Covariates

Child Gender

  Male

3740

50.4

  Female

3670

49.6

Child Gestation

  ≥ 37 weeks

6982

94.2

  < 37 weeks

428

5.8

Child Birthweight

  ≥ 2500 g

6970

94.0

  < 2500 g

349

4.7

  Missing

91

1.3

Maternal psychiatric history

  No

5955

80.4

  Yes

829

11.2

  Missing

626

8.4

Maternal smoking (any point in pregnancy)

  No

5073

68.5

  Yes

1488

20.1

  Missing

849

11.4