A total of 300 pregnant women and 300 women of reproductive age (controls) were selected from regions with a dietary iodine excess to evaluate thyroid and autoimmune thyroid functions. Fasting morning urine and venous blood samples were collected. Urinary iodine concentration, serum free tri-iodothyronine (FT₃), free thyroxine (FT₄), sensitive thyroid stimulating hormone, serum thyroid peroxidase antibody, and thyroglobulin antibody (TGAb) levels were determined. Iodine levels were excessive in 83.7% of pregnant women and 80.7% of the control women. The former showed lower rates of total thyroid disease and subclinical hypothyroidism than the latter (respectively, 21.7% vs 29.7%, P < .05; 19.7% vs 27.3%, P < .05). The FT₃ level, FT₄ level, and TGAb positive rates of pregnant women were lower than that in the controls (P < .05). Thus, both excessive iodine intake and pregnancy can influence the thyroid and autoimmune thyroid functions of women.