Objective  To investigate the correlation between blood glucose and thyroid-stimulating hormone (TSH) during gestation and evaluate the role of thyroid hormones and thyroid autoantibodies levels during gestation in screening gestational diabetes mellitus (GDM). Methods  A total of 265 women with 14-28 weeks of pregnancy who were examined at the First Affiliated Hospital of Chongqing Medical University were randomly selected. Levels of serum TSH, free triiodothyronine (FT₃), free thyroxine (FT₄), and thyroid peroxidase antibodies (TpoAb) were detected. The 75 g OGTT examination was performed in 28th week of pregnancy. The incidence of GDM was recorded. Spearman rank correlation analysis was adopted to analyze the correlation between the incidence of GDM and TpoAb level and between TSH and blood glucose level at each time point of OGTT. Results  ①The incidence of GDM in second trimester of pregnancy was 19.2%, the overall incidence of abnormal thyroid function was 3.8%, and the positive rate of TpoAb was 6.8%. ②The incidence of GDM in second trimester of pregnancy did not correlate with TSH. ③The incidence of GDM in second trimester of pregnancy did not correlate with whether TpoAb was positive (P=0.774). ④The differences of thyroid function and autoantibodies between women with GDM and without GDM were not significant. Conclusion  There is no obvious evidence that supports the correlation between thyroid disease and GDM. Two diseases should be screened separately to avoid misdiagnosis.