FT3 to FT4 ratio

This case-control study aimed to examine the associations between free triiodothyronine (fT3) levels and the fT3/fT4 ratio with the risk of gestational diabetes mellitus (GDM). Conducted across 12 US clinical centers, the study included 107 GDM cases and 214 non-GDM controls from a multiracial pregnancy cohort. Thyroid markers (fT3, fT4, TSH) were measured at different stages of pregnancy, and the fT3/fT4 ratio was derived. The study found that both fT3 levels and the fT3/fT4 ratio were positively associated with GDM. Specifically, the highest quartile of fT3 was associated with a significantly increased risk of GDM, with adjusted odds ratios (OR) of 4.25 at the first trimester and 3.89 at the second trimester. The risk estimates for the fT3/fT4 ratio were even higher, at 8.63 and 13.60 for the first and second trimesters, respectively. However, neither TSH nor fT4 was significantly associated with GDM. These findings suggest that elevated fT3 levels, possibly resulting from increased conversion of fT4 to fT3, may be an early indicator of GDM risk.