Background: Both iodine deficiency and iodine excess can harm the thyroid glands during pregnancy. In areas without iodine fortification, the relationship between the water iodine concentration (WIC) and thyroid disease in pregnant women requires further investigation.
Objective: The aim of this study was to evaluate the relationship between water iodine levels and the prevalence of thyroid disease in pregnant women residing in areas with high water iodine levels without access to iodized salt.
Methods: A cross-sectional survey was conducted in Shandong Province. Water and urine samples were collected, and the iodine content was assessed. Venous blood samples were taken to measure thyroid hormones and antibodies. Ultrasound was used to assess thyroid size and detect nodules.
Results: A total of 1073 pregnant women were included in this study. As the WIC increased, the urinary iodine concentration also increased, according to linear regression analysis (β=0.5; P<0.001). The lowest prevalence of subclinical hypothyroidism (SH) and thyroid dysfunction (TD) was observed at a WIC of 10-40 μg/L, while the lowest prevalence of thyroid nodules (TN) and goiter was seen at a WIC of 40-100 μg/L. Logistic regression analysis showed that WIC was significantly associated with thyroid diseases. WIC<10 μg/L was associated with TD prevalence (OR: 1.8; 95% CI: 1.1, 3.1), and WIC>100 μg/L was associated with SH, TN, and goiter prevalence (OR [SH]: 10.8; 95% CI: 1.4, 84.0; OR [TN]: 2.5; 95% CI: 1.1, 5.6; OR [goiter]: 2.4; 95% CI: 1.1, 5.6).
Conclusions: WIC is associated with thyroid function among pregnant women. WIC<10 μg/L is a risk factor for TD, while WIC>100 μg/L is a risk factor for SH, TN, and goiter. These findings suggest that intermediate WICs are most conducive to thyroid health in pregnant women, and that assessing local WICs could help improve maternal health.
Keywords: pregnant women; subclinical hypothyroidism; thyroid disease; thyroid nodule; water iodine concentration.
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