Table 1 Baseline characteristics

Age at inclusion (years)

30.1

4.8

28.5

4.9

<0.01

BMI pre-pregnancy

24.5

4.6

25.5

6.0

0.04

Socio-economic position (PCA-score)

0.04

1.0

−0.3

1.0

<0.01

n

%

n

%

P-value³

Ethnicity

<0.01

 Western^a

308

(43.4)

28

(24.6)

 South Asian^b

168

(23.7)

32

(28.1)

 Middle Eastern^c

105

(14.8)

21

(18.4)

 Other ethnicity^d

128

(18.1)

33

(28.9)

Education

0.02

  < 10 years

108

(15.3)

25

(22.5)

 10–12 years

274

(38.8)

50

(45.1)

 University or college

324

(45.9)

36

(32.4)

 Unknown

3

3

Occupation

0.04

 Elementary occupations and homemeakers

193

(27.8)

43

(39.1)

 Clerical/care occupations

245

(35.2)

37

(33.6)

 Manager/degree occupations

257

(37.0)

30

(27.3)

 Unknown

14

4

Parity

0.15

 None (nulliparous)

331

(46.7)

50

(43.9)

 1 (uniparous)

246

(34.7)

34

(29.8)

  ≥ 2 (multiparous)

132

(18.6)

30

(26.3)

Housing

0.53

 Flat

566

(81.0)

91

(83.5)

 Semi-detached or detached housing

133

(19.0)

18

(16.5)

 Unknown

10

5

Health pre-pregnancy

0.03

 Poor/not too good

71

(10.1)

17

(15.6)

 Good

354

(50.4)

62

(56.9)

 Very good

278

(39.5)

30

(27.5)

 Unknown

6

5

Smoking behaviour pre-pregnancy

0.51

 Non-smoker

579

(82.1)

94

(84.7)

 Daily or irregular smoker

126

(17.9)

17

(15.3)

 Unknown

4

3