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Table 2 Demographics and baseline characteristics by study cohort

From: Facilitating safety evaluation in maternal immunization trials: a retrospective cohort study to assess pregnancy outcomes and events of interest in low-risk pregnancies in England

Parameter

AP cohort N = 298 155

AP24+ cohort N = 208 328

LR cohort N = 137 932

Duration of pregnancy, days

 Mean (SD)

221 (89.3)

276 (13.9)

277 (13.4)

 Median (IQR)

273 (84.0–280.0)

280 (273.0–280.0)

280 (273.0–281.0)

Maternal age, years

 Mean (SD)

30 (6.2)

30 (5.8)

30 (5.7)

 Median (IQR)

30 (25.0–35.0)

30 (26.0–34.0)

30 (26.0–34.0)

Maternal age group, n (%)

 18–24 years

64 282 (21.6)

40 102 (19.2)

25 770 (18.7)

 25–29 years

73 199 (24.6)

54 429 (26.1)

35 746 (25.9)

 30–34 years

85 923 (28.8)

65 489 (31.4)

44 713 (32.4)

 35–39 years

56 947 (19.1)

39 366 (18.9)

26 076 (18.9)

 40–45 years

17 804 (6.0)

8 942 (4.3)

5 627 (4.1)

Ethnicity, n (%)

 White

252 166 (84.6)

178 527 (85.7)

115 810 (84.0)

 Asian

16 757 (5.6)

12 054 (5.8)

8 918 (6.5)

 Black

8 821 (3.0)

5 672 (2.7)

4 071 (3.0)

 Mixed

3 528 (1.2)

2 320 (1.1)

1 518 (1.1)

 Other

6 277 (2.1)

4 360 (2.1)

3 342 (2.4)

 Unknown

10 606 (3.6)

5 395 (2.6)

4 273 (3.1)

Index of Multiple Deprivation, n (%)

 1 (least deprived)

61 945 (20.8)

44 577 (21.4)

30 724 (22.3)

 2

58 360 (19.6)

41 240 (19.8)

27 772 (20.1)

 3

58 758 (19.7)

40 881 (19.6)

27 328 (19.8)

 4

59 246 (19.9)

40 908 (19.6)

26 604 (19.3)

 5 (most deprived)

59 612 (20.0)

40 573 (19.5)

25 415 (18.4)

 Missing

234 (0.1)

149 (0.1)

89 (0.1)

Year of pregnancy start, n (%)

 2004 a

16 027 (5.4)

14 041 (6.7)

10 040 (7.3)

 2005

27 609 (9.3)

19 220 (9.2)

13 456 (9.8)

 2006

28 221 (9.5)

19 706 (9.5)

13 527 (9.8)

 2007

29 076 (9.8)

20 268 (9.7)

13 830 (10.0)

 2008

29 761 (10.0)

20 382 (9.8)

13 709 (9.9)

 2009

29 342 (9.8)

20 125 (9.7)

13 421 (9.7)

 2010

27 983 (9.4)

19 479 (9.4)

12 763 (9.3)

 2011

27 209 (9.1)

19 073 (9.2)

12 349 (9.0)

 2012

24 661 (8.3)

16 888 (8.1)

10 688 (7.7)

 2013

20 812 (7.0)

14 269 (6.8)

8 982 (6.5)

 2014

16 166 (5.4)

10 959 (5.3)

6 697 (4.9)

 2015

11 514 (3.9)

7 903 (3.8)

4 856 (3.5)

 2016

8 580 (2.9)

5 954 (2.9)

3 589 (2.6)

 2017 a

1 194 (0.4)

61 (0.0)

25 (0.0)

  1. AP All Pregnancies, AP24+ All Pregnancies with gestational age ≥ 24 weeks, IQR interquartile range, LR Low-Risk pregnancies, n number of pregnancies in the specified category, N number of pregnancies included in the analysis in each cohort, SD standard deviation
  2. a Because the study start date was 1 January 2005, the number of pregnancies reported as starting in 2004 includes only those which began in the last 9 months of 2004 (if full term, for example). Conversely, because the study period end date was 31 December 2017 (with pregnancy end date up until 2 October 2017, as there was a requirement for at least a 90-day follow-up after the pregnancy end date), the number of pregnancies reported as starting in 2017 includes only those which began in the first month of 2017 (if full term, for example)
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