Iodine Nutrition Status and Its Association with Thyroid Function in First Trimester of Pregnancy in Southern China

Background Iodine is an essential trace element for pregnant women, and iodine deficiency was still reported in some areas worldwide. Shenzhen is located in southern China where is a coastal city and an iodine sufficient urban area, but there are not large-scale studies related to iodine nutrition status and thyroid function currently. Objectives The aims of our present study were to analyse the iodine nutrition status, and explore the potential associations between UIC and thyroid function during the first trimester of pregnancy in southern China. Methods In this cohort study, 14327 pregnant women during the first trimester were enrolled. Urinary Iodine Concentration (UI), Thyroid-Stimulating Hormone (TSH), Free Thyroxine (fT4), and Thyroid Peroxidase Antibody (TPOAb) were measured. The associations between thyroid function and Iodine nutrition status were estimated. Results The median UIC during the first trimester was 173.5 (118.2-247.5) µg/L, deficiency iodine status was observed in 39.3%. The UIC was negatively associated with TPO ( r= -0.034, P  = 0.000). Thyroid dysfunction incidence was 32.97%, Autoimmune Thyroid Disease is the most prevalent one (52.48%). The participants with Thyroid Dysfunction showed higher age ( t= -3.856, P  = 0.000) and lower UIC ( χ ²   =  26.079, P  = 0.000). ≥35 years old ( β =  0.102, P =  0.041, OR =  1.108,95% CI =  1.004–1.221), severe deficiency Iodine status ( β =  0.224, P =  0.007, OR =  1.251,95% CI =  1.062–1.473) and excess Iodine status ( β=- 0.430, P =  0.000, OR =  0.651,95% CI =  0.524–0.807) were the main determinants of thyroid dysfunction in our study cohort. Conclusions There were 39.3% incidence of deficiency iodine and 32.97% incidence of thyroid dysfunction in first trimester of pregnancy in southern China, where is an iodine sufficient urban area. The UIC was negatively associated with TPO. Higher age, severe deficiency and excess Iodine status were the main determinants of thyroid dysfunction. Additional studies of the Iodine nutrition status and dietary factors that can contribute to the prevention of thyroid dysfunction diseases in pregnant women living in iodine sufficient area are needed.