RESUMEN
AIM: The aim of this study is to examine gestational serum thyroid hormone levels and influencing factors among Chinese pregnant women with high dietary iodine intake. METHODS: The study was conducted from 2011 and 2013 in Zhoushan Women & Children's Hospital, Zhejiang, China. A total of 1991 pregnant women were enrolled and their serum levels of free thyroid hormones (FT4, FT3, and TSH) were detected by chemiluminescence method. RESULTS: Gestational serum FT4 and FT3 decreased with gestational week while TSH increased. Furthermore, the prevalence rate of subclinical hypothyroid increased with gestational stages, especially in the third trimester. Women aged more than 30 years had lower FT4 and FT3 in the first trimester and lower FT4 in the second trimester. No significant difference was found in the association of gestational serum thyroid hormones with maternal height and the gender of fetuses. CONCLUSION: Gestational serum thyroid hormones significantly changed with gestational week and were associated with the age of women. Specific normal range of thyroid hormones might be modified so as to better evaluate the thyroid hormone levels of pregnant women during pregnancy.