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Table 1 Sample characteristics and distribution of variables included in regression models across levels of pre-pregnancy BMI (N = 7564)

From: Overweight and obese pre-pregnancy BMI is associated with higher hospital costs of childbirth in England

Variables Total N (%) Pre-Pregnancy Body Mass Index P-value (Χ2)
Underweight N (%) Normal weight N (%) Overweight N (%) Obese Class I N (%) Obese Class II & III N (%)
Total 7564 (100.0%) 473(5.5%) 4897(66.0%) 1502(19.5%) 488(6.4%) 204(2.6%)  
Education
 None of these 1465 (15.4%) 163 (31.9%) 873 (13.9%) 305 (15.8%) 85 (13.9%) 39 (17.9%) < 0.0001
 GCSE/A level 4260 (57.5%) 244 (54.1%) 2714 (56.2%) 866 (59.5%) 306 (64.9%) 130 (64.1%)
 Higher education 1839 (27.1%) 66 (14.0%) 1310 (29.9%) 331 (24.7%) 97 (21.2%) 35 (18.0%)
Marital status
 Couple 4545 (60.9%) 205 (38.7%) 2934 (61.2%) 946 (63.2%) 330 (68.1%) 130 (65.9%) < 0.0001
 Single 3019 (39.1%) 268 (61.3%) 1963 (38.8%) 556 (36.8%) 158 (31.9%) 74 (34.1%)
OECD equivalised income quintile
 1st (lowest) 1570 (16.5%) 185 (34.92%) 979 (15.6%) 294 (19.6%) 73 (15.0%) 41 (16.4%) < 0.0001
 2nd 1605 (18.4%) 138 (27.28%) 918 (16.4%) 347 (23.1%) 141 (28.9%) 62 (28.1%)
 3rd 1473 (20.4%) 70 (18.25%) 944 (19.8%) 309 (20.6%) 107 (22.0%) 43 (22.1%)
 4th 1440 (21.2%) 37 (7.69%) 964 (19.7%) 300 (20.0%) 100 (20.5%) 39 (22.4%)
 5th (highest) 1476 (23.5%) 43 (11.33%) 1092 (26.5%) 252 (16.8%) 67 (13.7%) 22 (11.0%)
Ethnicity
 White 6259 (90.1%) 340 (83.2%) 4137 (91.2%) 1208 (88.7%) 397 (88.4%) 177 (92.7%) < 0.0001
 Mixed/Other 249 (2.5%) 28 (3.7%) 157 (2.4%) 45 (2.1%) 15 (3.0%) 4 (1.4%)
 Indian/ Pakistani/Bangladeshi 794 (5.2%) 88 (9.7%) 471 (4.8%) 176 (6.2%) 45 (4.4%) 14 (2.9%)
 Black Caribbean or Black African 262 (2.2%) 17 (3.4%) 132 (1.6%) 73 (3.0%) 31 (4.2%) 9 (3.0%)
Government Office Region*
 North 2345 (29.7%) 158 (32.5%) 1523 (29.8%) 460 (29.4%) 139 (27.9%) 65 (28.9%) 0.40
 Midlands & East 2391 (30.9%) 138 (27.2%) 1505 (30.3%) 504 (32.0%) 171 (33.9%) 73 (30.9%)
 London 1213 (13.8%) 90 (16.2%) 793 (13.9%) 231 (13.7%) 77 (13.4%) 22 (13.8%)
 South 1615 (25.6%) 87 (24.1%) 1076 (26.0%) 307 (24.9%) 101 (24.8%) 44 (26.5%)
Premature
 No 7055 (93.4%) 428 (90.4%) 4575 (93.7%) 1419 (94.2%) 457 (93.4%) 176 (85.7%) 0.0002
 Yes 509 (6.6%) 45 (9.6%) 322 (6.3%) 83 (5.8%) 31 (6.6%) 28 (14.3%)
Parity
 Primiparae 7291 (96.5%) 444 (93.6%) 4747 (97.0%) 1445 (96.0%) 466 (95.5%) 189 (93.2%) 0.001
 Multiparae 273 (3.5%) 29 (6.4%) 150 (3.0%) 57 (4.0%) 22 (4.5%) 15 (6.8%)
Notional cost of treatment (UK£)
 1–250 11 (0.2%) 1 (0.2%) 5 (0.2%) 3 (0.2%) 2 (0.6%) 0 (0.00%) < 0.0001
 250–500 1126 (14.9%) 86 (17.7%) 747 (15.7%) 218 (14.1%) 58 (10.9%) 17 (9.2%)
 500–750 3615 (47.7%) 238 (51.8%) 2.394 (48.5%) 695 (47.3%) 198 (39.9%) 90 (42.5%)
 750–1000 1701 (22.7%) 93 (18.7%) 1108 (22.8%) 331 (22.4%) 126 (27.0%) 43 (20.2%)
 1000–1250 656 (8.8%) 28 (5.9%) 385 (8.0%) 151 (9.8%) 59 (12.4%) 33 (18.6%)
 1250–1500 221 (2.8%) 12 (2.2%) 126 (2.5%) 54 (3.3%) 26 (5.5%) 3 (1.1%)
 1500–1750 85 (1.1%) 5 (1.1%) 46 (0.9%) 21 (1.3%) 6 (1.2%) 7 (3.1%)
 1750–2000 43 (0.6%) 2 (0.5%) 21 (0.4%) 12 (0.8%) 3 (0.5%) 5 (3.0%)
 2000 or over 106 (1.2%) 8 (1.8%) 65 (1.2%) 17 (0.9%) 10 (2.0%) 6 (2.4%)
  Mean (SE) Mean (SE) Mean (SE) Mean (SE) Mean (SE) Mean (SE) Mean (SD)
Maternal age (years) 28.8 (0.2) 25.0 (0.3) 28.8 (0.2) 29.4 (0.2) 29.3 (0.3) 29.8 (0.4) < 0.0001
Length of stay (days) 2.8 (0.1) 2.6 (0.2) 2.7 (0.1) 2.9 (0.1) 3.4 (0.2) 3.8 (0.3) < 0.0001
  1. Abbreviations: N Number of women, SE Standard error
  2. *North includes: North East, North West, Yorkshire & the Humber, Northern Ireland, and Wales; South Includes: South East and South West; Midland and East include: East Midlands, West Midlands, and East of England