Iodine, as the main raw material for the synthesis of thyroid hormones in the body, exhibits a U-shaped curve relationship with thyroid function. Both iodine deficiency and excess may cause thyroid dysfunction and damage human health. China was once one of the countries where iodine deficiency were widely prevalent in the world. Since the implementation of universal salt iodization in 1995, the iodine nutritional status in China has been greatly improved, and the goal of eliminating iodine deficiency disorders has been basically achieved. However, there is still a state of inadequate iodine nutrition among susceptible populations (pregnant women, breastfeeding mothers and infants). Pregnancy is a special physiological stage for women, and in order to meet the iodine needs of themselves and their fetuses, the iodine requirement of pregnant women increases by about 50% compared to non-pregnant women. WHO/UNICEF/ICCIDD suggest using urinary iodine concentration (UIC) to evaluate iodine nutritional status during pregnancy, with UIC of 150 - < 250 μg/L is considered suitable for iodine nutrition, but the best method for evaluating iodine nutrition status during pregnancy is still controversial. With the improvement of socio-economic level and people's health awareness, especially during special stages such as pregnancy, people pay more attention to individual iodine status. Therefore, the investigation of reliable indicators for evaluating iodine nutrition during pregnancy has gained increasing significance.

Objective:To evaluate the effect of oral iodized oil pills on iodine nutrition and thyroid function of pregnant women in Xinjiang Uygur Autonomous Region (Xinjiang).Methods:From May to July 2017, one county was selected from Ili Prefecture without taking iodized oil pills, Aksu Prefecture taking iodized oil pills once a year, and Kashgar Prefecture taking iodized oil pills twice a year in Xinjiang as survey sites, respectively; 100 pregnant women (evenly distributed in early, middle and late pregnancy) were selected from each survey county, the general data, urine and blood samples were collected, and urinary iodine and thyroid function indicators [free triiodothyronine (FT 3), free thyroxine (FT 4), thyrotropin (TSH), anti thyroglobulin antibody (TgAb), and anti thyroid peroxidase antibody (TPOAb)] were tested. Results:A total of 308 pregnant women were investigated, and 289 were finally included in the analysis, with an average age of 25 years; the body mass index (BMI) was (22.69 ± 3.07) kg/m 2. The occupation distribution was mainly farmer, accounting for 93.77% (271/289); most of them had junior high school education or below, accounting for 71.97% (208/289). The median urinary iodine of early, middle and late pregnant women in Kashgar Prefecture was 712.87, 604.50 and 656.23 μg/L, respectively, which were in iodine excess state. The iodine nutrition level of early pregnant women in Ili Prefecture and Aksu Prefecture was in iodine super suitability state, and the iodine nutrition level of middle and late pregnant women was in the iodine suitability state. The difference of median urinary iodine in early, middle and late pregnancy women between different regions was statistically significant ( Z = 53.02, 49.60, 44.66, P < 0.001). In addition, the urinary iodine of women in Kashgar Prefecture during each pregnancy period was significantly higher than that in Ili Prefecture and Aksu Prefecture ( P < 0.05). There were statistically significant differences in the levels of FT 3 among women in early pregnancy, FT 4 and TSH among women in middle pregnancy between different regions ( F = 4.59, 10.92, Z = 8.61, P < 0.05 or < 0.001). Among them, the level of FT 3 in early pregnancy in Kashgar Prefecture was lower than that in Ili Prefecture ( P < 0.05); the level of FT 4 in Kashgar Prefecture during middle pregnancy was higher than that in Ili Prefecture, and the level of TSH was lower than that in Ili Prefecture ( P < 0.05). There was no significant difference in TgAb positive rate, TPOAb positive rate and double antibody positive rate of early, middle and late pregnant women between different regions ( P > 0.05). The detection rates of hypothyroxinemia in early pregnant women in Ili Prefecture, Aksu Prefecture and Kashgar Prefecture were 13.9% (5/36), 3.2% (1/31) and 0 (0/33), respectively, and there was a statistically significant difference between different regions ( P = 0.036). The detection rates of subclinical hyperthyroidism in middle pregnant women were 0 (0/35), 0 (0/40), 17.6% (6/34), respectively, and there was a statistically significant difference between different regions ( P = 0.001). Conclusions:The results of urinary iodine in the three regions are in line with the iodine nutrition distribution under their respective iodine supplement strategies. Pregnant women in Kashgar Prefecture present iodine excess status after taking iodized oil pills; at the same time, the serum FT 3, FT 4 and TSH levels of pregnant women in Kashgar Prefecture are affected by iodine nutrition levels. Although it is scientific and effective to implement the intensified iodine supplement measures for pregnant women, it is still necessary to further study the suitability of oral iodine oil pills to ensure that pregnant women are at an suitability iodine nutrition level.