Iodine status of pregnant women in the Chinese plateau area – effects on thyroid function as well as adverse pregnancy and fetal outcomes

BACKGROUND AND OBJECTIVES: This study investigated the iodine status of pregnant women at an average altitude of approximately 2000 meters in Qujing, China. The relationship between iodine and thyroid function in different trimesters as well as adverse pregnancy and fetal outcomes were also investigated. METHODS AND STUDY DESIGN: A total of 1,025 pregnant women who were admitted to Qujing Affiliated Hospital of Kunming Medical University from January 2019 to August 2021 were included. Urinary iodine concentration (UIC) was detected by colorimetric method, and serum thyroid function was detected by chemiluminescence. Among them, 537 pregnant women were followed up to analyze the association of iodine with adverse pregnancy and fetal outcomes. RESULTS: The median UIC was 127 μg/L. Serum triiodothyronine, thyroxine, free triiodothyronine, and free thyroxine were negatively associated with urinary iodine concentration in the first and second trimesters of pregnancy. The proportion of pregnant women testing positive for thyroid peroxidase antibody (TPO-Ab) and the prevalence of thyroid autoimmunity (TAI) increased significantly in more-than-adequate iodine and excess iodine groups. Logistic regression analysis showed maternal iodine was not associated with adverse pregnancy and fetal outcomes. CONCLUSIONS: Mild iodine deficiency is common among pregnant women in plateau areas of China. The relationship between iodine and thyroid function is significant in the first and second trimesters of pregnancy, especially in those with moderate to severe iodine deficiency. Abnormal iodine level in pregnant women was not significantly associated with adverse pregnancy and fetal outcomes in areas with predominantly mild iodine deficiency.