High Water Iodine Concentrations Are Associated With the Prevalence of Subclinical Hypothyroidism, Thyroid Nodules, and Goiter Among Pregnant Women in Shandong, China

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.

Objectives

The aim of this study was to evaluate the relationship between WICs and the prevalence of thyroid disease in pregnant women residing in areas with high WICs 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, whereas the lowest prevalence of thyroid nodules (TNs) 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 of <10 μg/L was associated with TD prevalence (OR: 1.8; 95% CI: 1.1, 3.1), and WIC of >100 μg/L was associated with SH, TN, and goiter prevalence (SH—OR: 10.8; 95% CI: 1.4, 84.0; TN—OR: 2.5; 95% CI: 1.1, 5.6; goiter—OR: 2.4; 95% CI: 1.1, 5.6).

Conclusions

WIC is associated with thyroid function among pregnant women. WIC of <10 μg/L is a risk factor for TD, whereas WIC of >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.