Table 1.
Distributions of maternal urinary analytes and serum thyroid hormones.
| Analyte | n | Mean ± SD | Minimum | Percentile | Maximum | ||
|---|---|---|---|---|---|---|---|
| 25th | 50th | 75th | |||||
| Urine perchlorate (μg/L) | 1,880 | 8.49 ± 9.86 | 0.23 | 3.95 | 6.50 | 9.96 | 177.00 |
| Urine thiocyanate (μg/L) | 1,880 | 1,353 ± 1,553 | 20 | 459 | 898 | 1,590 | 16,200 |
| Urine nitrate (mg/L) | 1,876 | 66.5 ± 57.0 | 0.7 | 32.9 | 55.5 | 84.3 | 796.0 |
| Urine iodide (μg/L) | 1,818 | 214.9 ± 247.3 | 0.8 | 77.0 | 154.5 | 270.0 | 3,000 |
| Urine creatinine (mg/dL) | 1,878 | 131.5± 75.7 | 7.9 | 73.3 | 120.9 | 175.0 | 472.5 |
| Serum total T4 (μg/dL)b | 1,880 | 12.31 ± 1.89 | 0.56 | 11.21 | 12.26 | 13.40 | 19.99 |
| Serum TSH (μIU/mL)b | 1,879 | 1.36 ± 0.86 | 0.003 | 0.80 | 1.20 | 1.69 | 8.39 |
| Serum fT4 (ng/dL)b | 1,880 | 0.86 ± 0.19 | 0.11 | 0.77 | 0.85 | 0.93 | 5.44 |
| TG antibody (IU/mL) | 1,879 | 3.11 ± 24.13 | 0.00 | 0.00 | 0.00 | 0.60 | 565.90 |
| TPO antibody (IU/mL) | 1,876 | 12.90 ± 59.73 | 0.10 | 0.50 | 0.80 | 1.50 | 704.90 |
| Urine collection (week) | 1,878 | 8.6 ± 5.2 | 0.1 | 5.7 | 7.1 | 10.0 | 42.9 |
| Serum collection (week) | 1,880 | 17.1 ± 1.5 | 9.1 | 16.1 | 17.0 | 18.0 | 26.0 |
| Urine-serum difference (weeks)a | 1,878 | 9.2 ± 3.8 | 0.0 | 7.0 | 9.9 | 11.6 | 26.7 |
| Abbreviations: fT4, free thyroxine; T4, total thyroxine; TG, thyroglobulin; TPO, thyroperoxidase; TSH, thyroid-stimulating hormone. aAbsolute difference between urine and serum collection times. Seventy-two participants (3.8%) had their urine samples collected after their serum samples. The mean urine-serum difference considering these negative values was 8.4 ± 5.2 weeks; range, –26.7–19.3 weeks. bReference ranges from the University of Washington for all ages and both sexes are 4.8–10.8 μg/dL for total T4; 0.6–1.2 ng/dL for fT4, and 0.4–5.0 μIU/mL for TSH. The American Thyroid Association upper reference range for TSH in the second trimester of pregnancy is 3.0 μIU/mL (Garber et al. 2012). | |||||||