ABSTRACT
Objective:To investigate the impact of switching to low iodine drinking water in areas with high water iodine levels on the iodine nutritional status and thyroid function of pregnant women.Methods:A cross-sectional survey was conducted in Gaoqing County, Zibo City, Shandong Province. Pregnant women who underwent prenatal examinations at the Obstetrics Clinic of Gaoqing County People's Hospital from 2019 to 2021 were selected as the survey subjects. With reference to the Criteria for the Classification of Water Source High Iodine Areas and High Iodine Disease Areas (GB/T 19380-2016), pregnant women with drinking water iodine > 100 μg/L were considered as the high water iodine group and ≤100 μg/L was the non-high water iodine group. Basic information, one random urine sample, fasting blood sample, 24-hour urine sample and drinking water sample of pregnant women were collected, and thyroid ultrasound examination was performed on pregnant women. Urinary iodine (UI) concentration (UIC) and drinking water iodine concentration (WIC) were measured by inductively coupled plasma mass spectrometry, and 24-hour urinary iodine excretion (UIE) and daily iodine intake (TII) of pregnant women were calculated. Serum thyroid hormone (TSH), free triiodothyronine (FT 3), free thyroxine (FT 4), thyroid peroxidase antibody (TPOAb) and anti-thyroid autoantibodies (TgAb) were determined by automatic chemiluminescence immunoassay. Creatinine (CR) was determined using deproteinized endpoint microplate method and UI/CR was calculate. Results:A total of 797 pregnant women were included, and the UIC was 150.2 (88.1, 281.3) μg/L, the iodine nutrition was generally at an appropriate level. Among them, 584 pregnant women in the non-high water iodine group had a UIC of 120.9 (74.9, 191.5) μg/L, which was at the iodine deficiency level; 213 pregnant women in the high water iodine group had a UIC of 321.1 (201.9, 569.1) μg/L, which was at the iodine super-appropriate level; the differences in WIC, UIC, UIE, TII, and UI/CR between the two groups were statistically significant ( Z = 21.63, 13.34, 15.14, 15.14, 11.81, P < 0.001). After stratification by different gestational periods, the differences were statistically significant when comparing WIC and TSH in pregnant women in the non-high water iodine group and UI/CR in pregnant women in the high water iodine group by gestational period ( H = 59.13, 7.30, 13.60, P < 0.05). A total of 744 pregnant women were tested for thyroid function, and 128 cases of TSH > 2.5 mU/L, 15 cases of hypothyroxemia, and 19 cases of subclinical hypothyroidism were detected, with detection rates of 17.2%, 2.0%, and 2.6%, respectively. The differences were statistically significant when comparing TSH and TPOAb levels and the proportion of pregnant women with TSH > 2.5 mU/L in the high water iodine and non-high water iodine groups ( Z = 3.04, - 2.17, χ 2 = 6.94, P = 0.002, 0.030, 0.008). The thyroid glands of pregnant women were examined in 720 cases, and 30 cases of goiter and 150 cases of thyroid nodules were detected, with detection rates of 4.2% and 20.8%, respectively. The median thyroid volume was 8.92 ml in the high water iodine group and 8.60 ml in the non-high water iodine group, which were both within the normal range, with no statistically significant difference between the groups ( Z = - 0.75, P = 0.455). Conclusions:After changing to low iodine water, the overall iodine nutrition of pregnant women in Gaoqing County is now at an appropriate level, and the reduction of water iodine effectively reduces the risk of TSH abnormalities in local pregnant women. However, pregnant women in the non-high water iodine group are iodine deficiency, and pregnant women in the high water iodine group are at iodine super-appropriate, and the iodine nutrition level of pregnant women in this area is highly variable, which causes the "illusion" that the overall iodine level of local pregnant women is suitable.