Table 1 Maternal characteristics according to urinary iodine-to-creatinine ratio
|  | All participants, n = 6637 | Iodine-to-creatinine ratio (sample split into thirds) | ||
|---|---|---|---|---|
Lower third (< 67 μg/g), n = 2213 | Middle third (67 to 105 μg/g), n = 2212 | Higher third (> 105 μg/g), n = 2212 | ||
I:Cr (μg/g), geometric mean (99% CI) | 86.0 (84.5 to 87.5) | 48.5 (47.8 to 49.3) | 83.4 (82.8 to 84.0) | 157.2 (154.3 to 160.2) |
I:Cr (μg/g), median (IQR) | 83.1 (59.4 to 121.2) | 51.4 (42.7 to 59.4) | 83.2 (74.4 to 93.3) | 146.1 (121.2 to 185.2) |
UIC (μg/L), geometric mean (99% CI) | 70.8 (69.1 to 72.5) | 45.9 (44.2 to 47.8) | 70.0 (67.6 to 72.6) | 110.4 (106.4 to 114.5) |
UIC (μg/L), median (IQR) | 76.2 (44.6 to 120.2) | 52.2 (29.1 to 78.0) | 77.4 (47.3 to 112.5) | 117.6 (71.8 to 178.8) |
Age (years), mean (SD) | 27.2 (5.6) | 26.5 (5.5) | 27.3 (5.6) | 27.8 (5.6) |
BMI (kg/m2), mean (SD) | 25.8 (5.5) | 26.5 (5.8) | 25.9 (5.4) | 25.1 (5.1) |
Socioeconomic status†| ||||
 Least deprived and most educated | 1241 (21) | 307 (16) | 429 (22) | 505 (25) |
 Employed, not materially deprived | 1231 (21) | 335 (17) | 440 (22) | 456 (23) |
 Employed, no access to money | 917 (16) | 320 (16) | 295 (15) | 302 (15) |
 Receives benefits, not materially deprived | 1594 (27) | 633 (32) | 505 (26) | 456 (23) |
 Most economically deprived | 920 (16) | 360 (18) | 293 (15) | 267 (13) |
Ethnic background, n (%) | ||||
 White British and European | 2877 (44) | 800 (36) | 1016 (46) | 1061 (48) |
 Pakistani | 2827 (43) | 1064 (48) | 914 (42) | 849 (39) |
 Others (Black, Indian, mixed, others) | 901 (14) | 337 (15) | 271 (12) | 293 (13) |
Parity | ||||
 0 | 2931 (44) | 933 (42) | 966 (44) | 1032 (47) |
 1 | 1859 (28) | 600 (27) | 623 (28) | 636 (29) |
 2 | 1059 (16) | 371 (17) | 361 (16) | 327 (15) |
 3+ | 788 (12) | 309 (14) | 262 (12) | 217 (10) |
Health and lifestyle in pregnancy | ||||
 Gestational diabetes, n (%) | 499 (8) | 152 (7) | 167 (8) | 180 (8) |
 Pre-pregnancy hypertension, n (%) | 50 (0.8) | 21 (1.0) | 17 (0.8) | 12 (0.5) |
 Pregnancy-induced hypertension, n (%) | 375 (6) | 125 (6) | 126 (6) | 124 (6) |
 Preeclampsia, n (%) | 173 (3) | 61 (3) | 55 (2) | 57 (3) |
 Drank any alcohol, n (%) | 958 (14) | 299 (14) | 335 (15) | 324 (15) |
 Smoked, n (%) | 969 (15) | 302 (14) | 352 (16) | 315 (14) |
 Used any supplements, n (%) | 1334 (20) | 213 (10) | 382 (17) | 739 (33) |
 Iodine-containing supplements, n (%) | 988 (15) | 123 (6) | 264 (12) | 601 (27) |
 White fish intake* (g/day), mean (SD) | 21.0 (27.0) | 18.7 (26.3) | 22.1 (28.2) | 22.1 (26.1) |
 Oily fish intake* (g/day), mean (SD) | 1.4 (3.8) | 1.0 (3.2) | 1.5 (4.2) | 1.7 (4.0) |
 Total fish intake* (g/day), mean (SD) | 23.8 (29.3) | 20.8 (28.3) | 25.1 (30.7) | 25.4 (28.8) |
Eat 5 fruits/vegetables per day*, n (%) | ||||
 Always | 422 (19) | 122 (16) | 160 (21) | 140 (19) |
 Sometimes | 1700 (75) | 601 (77) | 558 (72) | 541 (75) |
 Never | 151 (7) | 57 (7) | 52 (7) | 42 (6) |