Higher FT3/FT4 Ratio Linked to Increased Gestational Diabetes Risk, suggests study

A new study published in the journal of the Frontiers in Endocrinology showed that higher FT3/FT4 ratios in the early and middle stages of pregnancy were linked to aberrant lipid and glucose metabolism as well as an increased risk of gestational diabetes mellitus (GDM), indicating that they might be a helpful additional marker for early detection of GDM-risk women.

Thyroid indicators are an important area of clinical study since recent studies indicate that maternal thyroid function is critical to glucose regulation. The mother's body experiences significant physiological changes in the early to mid-stage of pregnancy, including crucial changes in thyroid hormone synthesis that are necessary to support the early growth of the fetus.

Recent research focuses on how minute changes in certain indicators, such free thyroxine (FT4), free triiodothyronine (FT3), and thyroid-stimulating hormone (TSH), may directly affect insulin sensitivity and metabolic pathways. In particular, an increased risk of developing GDM is increasingly associated with early imbalances, such as excessive TSH or reduced FT4 levels. This study looked at the relationships in a Chinese population between free T3 (FT3), thyroid autoimmunity, the FT3/free T4 (FT4) ratio, and GDM.

Between January 2023 and November 2025, 10,258 women were enrolled in this longitudinal cohort research at Shanghai First Maternity and Infant Hospital; 7,463 of those women were included in the final analysis. At 4–24 weeks of pregnancy, thyroid function was evaluated, and at 24–28 weeks, a 75-g oral glucose tolerance test (OGTT) was used to identify GDM.

FT3 and the FT3/FT4 ratio were positively correlated with GDM in the early (4–12 weeks) and mid-pregnancy (13–24 weeks). The percentiles of the FT3/FT4 ratio showed notable differences in lipid metabolism. While thyroglobulin antibody (TGAb), FT4, and TSH did not significantly correlate with GDM, thyroid peroxidase antibody (TPOAb) was linked to GDM only during the early stages of pregnancy.

Overall, the findings of this study suggest that FT3 levels and the FT3/FT4 ratios in early and mid-pregnancy are strongly correlated with the risk of GDM. These results offer a possible role for thyroid-related indicators in GDM risk stratification and advance knowledge of maternal thyroid-related metabolic changes during pregnancy.

Reference:

Liu, X., Zou, C., Shen, Q., Yang, Y., Liu, Y., Zhao, R., Chen, X., & Du, Q. (2026). Thyroid markers in early to mid-pregnancy and risk of gestational diabetes: a longitudinal retrospective cohort study. Frontiers in Endocrinology, 17(1799406), 1799406. https://doi.org/10.3389/fendo.2026.1799406