Table 1 Background data for the nulliparous women in the index and reference groups at the beginning of their pregnancy recorded from the antenatal record

Age when giving birth

0.047

<25

33

18.2

103

23.9

25-34

127

70.6

257

59.6

35-

21

11.6

71

16.5

BMI

0.016

<25.0

96

61.9

226

63.1

25-29.9

30

19.4

95

26.5

≥30.0

29

18.7

37

10.3

Missing

16

73

Employment group

0.047

High white collar worker

22

12.2

25

5.8

Low white collar worker

77

42.5

198

46.0

Blue collar worker

32

17.7

101

23.5

.

Unemployed

13

7.2

24

5.6

Other*

37

20.4

82

19.1

Smoking

0.665

Yes

35

19.3

90

20.9

No

146

80.7

341

79.1

Induced abortion

0.212

No

144

79.6

361

83.8

Yes

37

20.4

70

16.2

Spontaneous abortion

0.162

No

164

90.6

373

86.5

Yes

17

9.4

58

13.5