FT3 to FT4 ratio

This study explored the prospective associations between thyroid markers in early pregnancy and the risk of gestational diabetes mellitus (GDM), focusing on the potential mediating role of lipid species. The cohort included 6068 pregnant women, with thyroid markers such as free triiodothyronine (fT3), free thyroxine (fT4), thyroid-stimulating hormone, thyroid peroxidase antibody, and thyroglobulin antibody measured before 15 weeks of gestation. The fT3/fT4 ratio was used as a marker of deiodinase activity. Results showed that higher levels of fT4 were associated with a decreased risk of GDM, while a higher fT3/fT4 ratio was linked to an increased risk of GDM. Multiple linear regression revealed that the fT3/fT4 ratio was positively associated with several lipid species, including alkylphosphatidylcholine 36:1 and sphingomyelin 34:1. Mediation analysis suggested that 67.9% of the association between the fT3/fT4 ratio and GDM was mediated by these lipids. The findings indicate that lower fT4 levels or higher fT3/fT4 ratios in early pregnancy may be indicative of increased GDM risk, with lipid species playing a significant mediating role in this association.