Meryem Keçeci OĞUZHANOĞLU, Senem Karacabey ÇAKMAK
Anatolian Current Medical Journal - 2026;8(5):853-861
Aims: Whether levothyroxine replacement normalizes diabetes management in gestational diabetes mellitus (GDM) with co-existing hypothyroidism is unclear. We compared treatment requirements, glycemic control, lipid profile, and vitamin D status across GDM alone, GDM with treated hypothyroidism, and hypothyroidism alone. Methods: Prospective three-group cohort study of 240 pregnant women (80/group) assessed once at 24-28 weeks; hypothyroid patients were on stable levothyroxine (>=12 weeks). Groups were compared with Kruskal-Wallis/Chi-square tests (Bonferroni-corrected); the primary outcome was modeled by multivariable logistic regression (age, body-mass index, baseline glucose, gestational age). Results: Thyroid-stimulating hormone was higher in GDM+hypothyroidism than GDM-alone (1.99 vs. 1.51 uIU/ml; p=0.004). Lipid parameters did not differ between groups (all p>0.3). Diet therapy controlled glycemia in 22.5% of GDM+hypothyroidism versus 50.0% of GDM-alone; pharmacologic treatment was required in 77.5% versus 50.0% (p<0.001), persisting after adjustment (confidence interval 3.65, 95% confidence interval 1.58-8.39, p=0.002). Vitamin D was lower in both GDM groups than hypothyroidism-alone (p=0.003, p<0.001) but similar between the two GDM groups (p=0.484), arguing against an additive effect of co-existing GDM and hypothyroidism. Homeostasis Model Assessment for Insulin Resistance and insulin were higher in both GDM groups than hypothyroidism-alone (p<0.001, p=0.002) but similar between them (p=1.00), consistent with GDM driving insulin resistance. Hemoglobin A1c (HbA1c) did not differ across groups (p=0.089). Conclusion: Treated overt hypothyroidism was associated with higher pharmacologic treatment requirements in GDM, independent of confounders. Lipid parameters and HbA1c did not differ between groups; vitamin D was lower in both GDM groups without evidence of an additive effect. These findings identify GDM with treated hypothyroidism as a higher-risk subgroup warranting closer monitoring, pending confirmation in larger trials.
