Table 2 Effect of letter type on survey completion by maternal characteristics

Maternal age (years)

 ≤24

2.20

1.22–3.96

 25–29

1.30

0.91–1.86

0.04

 30–34

0.99

0.74–1.31

 ≥35

0.88

0.62–1.24

Country of birth

 Australia

1.06

0.84–1.33

0.54

 Other

1.19

0.90–1.57

Socio-economic index

 1 (lowest)

1.1

0.5–2.5

0.06

 2

1.9

1.2–2.9

 3

0.7

0.4–1.3

 4

1

0.7–1.4

 5 (highest)

1.1

0.8–1.4

Maternity unit

1.5

0.4–5.7

 1

1.33

0.97–1.82

0.11

 2

0.99

0.71–1.36

 3

0.30

0.06–1.50

 4

1.85

1.11–3.09

 5

1.14

0.60–2.17

 6

0.78

0.48–1.26

 7

1.52

0.40–5.71

Parity

 Nulliparous

1.15

0.89–1.49

 Multiparous

1.07

0.84–1.37

0.69

Maternal smoking in pregnancy

 No

1.11

0.93–1.33

0.59

 Yes

1.42

0.59–3.43

Maternal BMI

 ≤25

1.20

0.96–1.49

 >25, ≤ 30

0.62

0.42–0.90

<0.001

 >30

2.05

1.25–3.35

Multiple pregnancy

 No

1.11

0.93–1.33

 Yes

1.02

0.23–4.53

0.91

Mode of birth

 Vaginal

1.02

0.81–1.28

0.67

 Instrumental

1.26

0.76–2.09

 Pre-labour caesarean

1.29

0.82–2.05

 Intrapartum caesarean

1.27

0.80–2.02

Gestational age at birth (completed weeks)

 <37

1.26

0.64–2.48

 ≥37

1.10

0.92–1.32

0.70

Infant gender

 Male

1.05

0.81–1.34

 Female

1.17

0.91–1.52

0.52

Infant admission to intensive care or special care nursery

 No

1.11

0.92–1.35

0.83

 Yes

1.06

0.68–1.65