Objective To explore the association between iodine nutritional status and thyroid function among women at first trimester of pregnancy in Xi'an.

Methods Totally 6 510 pregnant women who registered at obstetric outpatient clinic, Northwest Women's and Children's Hospital were recruited as study subjects. Urinary iodine concentration and blood thyroid stimulating hormone (TSH), total triiodothyronine (TT4), total thyroxine (TT3), free triiodothyronine (FT3), free thyroxine (FT4), thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb) were tested in order to compare the difference of thyroid function and disease prevalence at different iodine nutrition levels and explore their association.

Results The median urine iodine (MUI) of early pregnant women in Xi'an was 216.15 μg/L. With the increase of urine iodine level, the levels of FT3, FT4, TT3 and TT4 increased and the positive rate of TgAb decreased significantly (all P < 0.05). Further multivariate Logistic regression analysis showed that iodine deficiency could increase the positive rate of TgAb (OR = 1.413, 95% CI: 1.086－1.839). There was no significant difference in TSH, TPOAb and the prevalence of thyroid diseases among different iodine nutrition levels (all P > 0.05). Iodine nutrition level was not the factor associated with thyroid diseases (P > 0.05).

Conclusion Iodine is adequate among pregnant women at first trimester of pregnancy in Xi'an. There is no association between iodine nutrition and thyroid diseases. Iodine deficiency is a risk factor for TgAb positive.