Table 1 Baseline characteristics of pregnancies included in the primary analysis and pregnancies of women with multimorbidity included in the subgroup analysis, followed up through their first trimester

 15–19

68,741 (8.46)

6344 (4.55)

 20–24

151,734 (18.68)

22,575 (16.19)

 25–29

225,289 (27.73)

37,982 (27.23)

 30–34

232,213 (28.59)

42,468 (30.45)

 35–39

113,694 (14)

24,537 (17.59)

 40–44

19,480 (2.4)

5080 (3.64)

 45–49

1203 (0.15)

485 (0.35)

 Underweight (<18.5)

28,295 (3.48)

5079 (3.64)

 Normal weight (18.5–24.9)

358,371 (44.12)

58,746 (42.12)

 Overweight (25–29.9)

164,972 (20.31)

31,156 (22.34)

 Obese (>30)

114,889 (14.14)

28,986 (20.78)

 Missing

145,827 (17.95)

15,504 (11.12)

 White

376,454 (46.3)

69,104 (49.6)

 Black

21,343 (2.6)

4905 (3.5)

 South Asian

22,597 (2.8)

3445 (2.5)

 Mixed race

4300 (0.5)

677 (0.5)

 Other race

12,745 (1.6)

2468 (1.8)

 Ethnicity data missing

374,915 (46.2)

58,872 (42.2)

 Non-smoker

440,868 (54.3)

68,644 (49.2)

 Ex-smoker

113,620 (14.0)

23,663 (17.0)

 Smoker

209,927 (25.8)

43,634 (31.3)

 Smoking status missing

47,939 (5.9)

3530 (2.5)

 1

243,736 (30.0)

34,083 (24.4)

 2

222,309 (27.4)

34,763 (24.9)

 3

153,286 (18.9)

27,182 (19.5)

 4

88,844 (10.9)

17,826 (12.8)

 5+

104,179 (12.8)

25,617 (18.4)

 England

522,802 (64.7)

87,511 (62.7)

 Northern Ireland

42,278 (5.2)

8127 (5.8)

 Scotland

145,258 (17.9)

25,336 (18.2)

 Wales

102,016 (12.6)

18,497 (13.3)

 1 (most deprived)

219,238 (26.99)

38,260 (27.43)

 2

169,268 (20.84)

27,983 (20.06)

 3

153,936 (18.95)

26,904 (19.29)

 4

133,756 (16.47)

22,659 (16.25)

 5 (least deprived)

136,156 (16.76)

23,665 (16.97)

Number of pre-existing comorbidities, mean (SD)

1.35 (1.48)

3.49 (1.47)