Association Between Maternal Thyroid-Stimulating Hormone Concentration in Early Pregnancy and Gestational Diabetes Mellitus: A Retrospective Cohort Study

Background: Although the association between thyroid function in early pregnancy and gestational diabetes mellitus (GDM) has been explored, evidence remains inconsistent. This inconsistency necessitates further investigation to better clarify the potential relationship between maternal thyroid function in early pregnancy and subsequent GDM risk. Methods: A total of 1589 healthy pregnant individuals were enrolled in this study, all of whom had their initial prenatal visit from 10 to 13+6 weeks of pregnancy at Suzhou Ninth Hospital affiliated to Soochow University from June to October 2023. Data were extracted from electronic medical records. GDM was diagnosed utilizing the 75 g oral glucose tolerance test (OGTT) at 24–28 weeks of gestation. To evaluate the independent association between early pregnancy thyroid function indicators and GDM, a series of analyses, including logistic regression, restricted cubic spline (RCS) analysis, correlation, and sensitivity analysis, was conducted. Results: Among 1589 pregnant women, 418 (26.31%) developed GDM. Multivariate logistic regression identified family history of diabetes, age, pre-pregnancy body mass index (BMI), fasting blood glucose (FBG), thyroid-stimulating hormone (TSH) (odds ratio [OR] = 1.23, 95% confidence interval [CI]: 1.09–1.38, p < 0.001), and triglycerides (TG) in early pregnancy as risk factors for GDM. RCS analysis demonstrated a significant dose-response correlation between TSH levels and GDM (p for overall association < 0.001, p for nonlinearity = 0.441). Subgroup analysis revealed that among pregnant individuals with pre-pregnancy BMI ≥24 kg/m2, each unit increase in early-pregnancy TSH was associated with a 1.61-fold increase in the odds of GDM (95% CI: 1.31–1.98, p < 0.001). Conclusions: Elevated odds of GDM may be associated with higher maternal TSH concentrations in the first trimester. This association was particularly pronounced among individuals with a pre-pregnancy BMI ≥24 kg/m2.