Table 1.
Descriptive characteristics of the study population (n = 39,471 mother–child pairs) by maternal iodine intake
| Iodine from food, non-supplement users | Iodine supplement use in pregnancy (week 0–22) | All | Whole MoBaa | ||||
|---|---|---|---|---|---|---|---|
| < 100 µg/day | 100–150 µg/day | > 150 µg/day | No | Yes | |||
| Study sample, n (%) | 8096 (21) | 9126 (23) | 7584 (19) | 24,806 (63) | 14,665 (37) | 39,471 (100) | 101,784 |
| Maternal age at delivery, mean (SD), years | 30.5 (4.4) | 30.8 (4.3) | 30.6 (4.5) | 30.6 (4.4) | 30.6 (4.4) | 30.6 (4.4) | 30.2 (4.6) |
| Pre-pregnancy BMI, mean (SD), kg/m2 | 24.1 (4.2) | 23.8 (4.0) | 23.9 (4.0) | 23.9 (4.0) | 23.7 (4.1) | 23.8 (4.1) | 24.0 (4.3) |
| Parity, % | |||||||
| 0 | 46 | 42 | 41 | 43 | 54 | 47 | 47 |
| 1 | 37 | 37 | 37 | 37 | 32 | 35 | 36 |
| 2 or more | 17 | 20 | 22 | 19 | 13 | 17 | 18 |
| Maternal education, % | |||||||
| ≤ 12 years | 27 | 24 | 27 | 26 | 22 | 24 | 32 |
| 13–16 years | 43 | 45 | 46 | 45 | 45 | 45 | 41 |
| > 16 years | 28 | 29 | 25 | 27 | 31 | 29 | 25 |
| Other/missing | 2.5 | 1.9 | 2.1 | 2.2 | 2.1 | 2.1 | 2.1 |
| Married/cohabitant, % | 97.1 | 97.5 | 96.9 | 97.2 | 96.9 | 97.1 | 96.1 |
| Smoking in pregnancy, % | |||||||
| Occasionally | 15 | 14 | 14 | 14 | 15 | 14 | 17 |
| Daily | 4.1 | 3.4 | 4.0 | 3.8 | 3.0 | 3.5 | 5.7 |
| Chronic illness, % | 11.1 | 8.7 | 8.4 | 9.4 | 10.8 | 9.9 | 10.2 |
| Household income, % | |||||||
| Low | 24 | 24 | 27 | 25 | 23 | 24 | 29 |
| Medium | 41 | 42 | 43 | 42 | 41 | 42 | 41 |
| High | 33 | 32 | 27 | 31 | 34 | 32 | 28 |
| Missing | 2.3 | 2.1 | 2.9 | 2.4 | 2.1 | 2.3 | 3.1 |
| Bilingual parent(s), % | 9.8 | 9.5 | 7.6 | 9.0 | 10.8 | 9.7 | 10.8 |
| Maternal history of reading/writing difficulties (%) | 6.2 | 4.8 | 5.4 | 5.4 | 5.4 | 5.6 | – |
| Child sex boy (%) | 51.4 | 51.1 | 51.5 | 51.3 | 50.2 | 50.9 | 51.2 |
| Iodine from food, median (IQR), µg/day | 78 (63, 89) | 123 (111, 136) | 182 (163, 212) | 122 (90, 161) | 121 (89, 160) | 122 (89, 161) | 121 (89, 161)b |
| UIC, median (IQR), µg/Lc | 47 (26, 85) | 62 (33, 105) | 70 (39, 116) | 59 (32, 101) | 83 (43, 138) | 67 (35, 115) | – |
| Urinary creatinine, median (90% range) g/Lc | 0.75 (0.17, 2.00) | 0.76 (0.16, 1.88) | 0.72 (0.21, 1.89) | 0.75 (0.17, 1.92) | 0.72 (0.16, 1.87) | 0.74 (0.17, 1.90) | – |
| UIC, median (IQR), µg/g creatininec | 69 (44, 97) | 83 (58, 115) | 99 (72, 132) | 83 (56, 115) | 116 (75, 187) | 91 (63, 139) | – |
| Iodine supplement (%) | 0 | 0 | 0 | 0 | 100 | 37 | 37b |
| Folic acid supplement (%)d | 71 | 71 | 68 | 70 | 84 | 75 | 69 |
| Omega 3 supplement (%) | 79 | 81 | 82 | 81 | 80 | 80 | 79b |
| Maternal energy intake, median (IQR), MJ | 8.0 (6.9, 9.3) | 9.2 (8.1, 10.6) | 11.0 (9.6, 12.8) | 9.3 (7.9, 11.0) | 9.3 (7.9, 11.0) | 9.3 (7.9, 11.0) | 9.4 (7.9, 11.1) |
aIncludes all pregnancies in the Norwegian Mother and Child Cohort Study with information on background characteristics from questionnaire 1
bIn singleton pregnancies with available data from the food frequency questionnaire (n = 83,721)
cIn a subsample of n = 2001 with data on urinary iodine and creatinine in gestational week 18
dUse of a folic acid supplement within the interval from 4 weeks before to 8 weeks after conception from questionnaire 1