Wang Y, Sun F, Wu P, et al. - In early pregnancy, lower serum free thyroxine (fT4) concentrations or higher free triiodothyronine (fT3)/fT4 ratio were correlated with an increased risk of gestational diabetes mellitus (GDM). The relationship between the fT3/fT4 ratio and GDM was largely mediated by specific lipid species.

• The Tongji-Shuangliu Birth Cohort included 6,068 pregnant women in this study.

• The participants' mean age was 26.6 ± 3.7 years, and their mean gestational age was 10.3 ± 2.0 weeks.

• After adjusting for potential confounders, higher levels of fT4 were correlated with a lowered risk of GDM, whereas a higher fT3/fT4 ratio was related to an increased risk of GDM.

• Multiple linear regression analysis revealed that the fT3/fT4 ratio was positively linked to alkylphosphatidylcholine 36:1, phosphatidylethanolamine plasmalogen 38:6, diacylglyceride 18:0/18:1, sphingomyelin 34:1, and phosphatidylcholine 40:7.

• Mediation analysis revealed that the composite effect of these lipids may account for 67.9% of the association between fT3/fT4 ratio and GDM.