TG

This study investigated the combined effects of free thyroxine (FT4) and triglyceride (TG) levels in early pregnancy on the risk of gestational diabetes mellitus (GDM) in 40,156 pregnant women. An L-shaped association between FT4 and GDM was observed, where lower FT4 levels, coupled with higher TG concentrations, significantly increased GDM risk (OR: 2.44, 95% CI: 2.14–2.80; P < 0.001). A significant interaction between FT4 and TG levels was detected (P = 0.036), with TG levels mediating 21.3% of the effect between FT4 and GDM. The findings suggest that managing both hypothyroidism and TG levels in early pregnancy may help reduce the risk of GDM.