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Reference Intervals of the Ratio of Urine Iodine to Creatinine in Pregnant Women in an Iodine-Replete Area of China

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Abstract

The assessment method of iodine nutrition for pregnant women lacks strong evidence-based medicine. The prevalence of iodine deficiency in pregnant women may be overestimated using urinary iodine concentration (UIC). The reference intervals of UIC-to-urinary creatinine concentration ratio (UIC/UCr) were established using a self-sequential longitudinal study of pregnant women with singleton gestation who were recruited using the criteria of the National Academy of Clinical Biochemistry in Dandong City, which is a long-term iodine-replete area. Nine thousand one hundred sixty-four pregnant women in the first trimester from Dalian City, Dandong City, and Shenyang City were included to verify our proposed reference intervals. UIC and concentrations of urinary creatinine, serum iodine, TSH, FT4, TPOAb, and TgAb were measured. The reference intervals of UIC/UCr were 38.63–489.46 μg/g for the first trimester, 58.48–644.03 μg/g for the second trimester, and 56.27–644.93 μg/g for the third trimester. The prevalence of iodine deficiency was 49.50% using UIC as the indicator (< 150 μg/L), while the prevalence was 3.28% using UIC/UCr (< 38.63 μg/g). The prevalence of iodine excess was 3.21% using UIC as the indicator (> 500 μg/L) while the prevalence was 1.45% using UIC/UCr (> 489.46 μg/g). The highest prevalence of overt hypothyroidism and positive thyroid antibodies was in the group with UIC/UCr < 38.63 μg/g. In contrast to the place of residence and age, BMI was an influencing factor for UIC/UCr. The reference intervals of UIC/UCr were established. UIC/UCr may eliminate the effect of urine volume and reflect the actual prevalence of iodine deficiency in pregnant women.

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Acknowledgments

We thank all the physicians of the gynecology and obstetrics clinics from the 13 hospitals and 6 prenatal clinics in Liaoning Province for their contribution. We also thank the residents for participating in this study.

Funding

This work was supported by the 973 Science and Technology Research Foundation, Ministry of Science and Technology, China (Grant no. 2011CB512112); projects of the Liaoning Province University Innovation Team (Grant no. LT2012015); the National Science and Technology Support Program (Grant no. 2014BAI06B00); the Chinese National Natural Science Foundation (Grant no. 81170730); the Liaoning Science Public Research Funds (Grant no. 2014001001/GY2014-A-001); the Research Foundation of the Department of Science and Technology of Liaoning Province Government, China (Grant nos. 2012225020 and 2011225023); and projects of the Key Laboratory of the Endocrine Diseases in Shenyang City (Grant no. F11-244-1-00).

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Authors and Affiliations

  1. Department of Endocrinology and Metabolism and the Institute of Endocrinology, The First Hospital of China Medical University, Shenyang, 110001, Liaoning, People’s Republic of China

    Jingyi Luo, Chenyan Li, Zhongyan Shan & Weiping Teng

  2. Department of Endocrinology and Metabolism, Peking University International Hospital, Beijing, 100000, People’s Republic of China

    Xiaomei Zhang

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  1. Jingyi Luo
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  2. Chenyan Li
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  3. Xiaomei Zhang
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  4. Zhongyan Shan
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  5. Weiping Teng
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Contributions

Jingyi Luo analyzed the data and wrote the paper. Chenyan Li and Xiaomei Zhang collected the samples and data. Zhongyan Shan and Weiping Teng interpreted the results. Weiping Teng contributed to the design of the study.

Corresponding author

Correspondence to Weiping Teng.

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All the research protocols were approved by the Medical Ethics Committee of China Medical University and were in keeping with the tenets of the Declaration of Helsinki. Informed consent was obtained from every participant before the study was started.

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Luo, J., Li, C., Zhang, X. et al. Reference Intervals of the Ratio of Urine Iodine to Creatinine in Pregnant Women in an Iodine-Replete Area of China. Biol Trace Elem Res 199, 62–69 (2021). https://doi.org/10.1007/s12011-020-02133-8

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