Evaluation of thyroid function tests and their association with complications in patients with gestational diabetes mellitus

ABSTRACT Evaluation of Thyroid Function Tests and Their Association with Complications in Patients with Gestational Diabetes Mellitus Objective: This study was conducted to evaluate the clinical findings and thyroid function tests of pregnant women with and without a diagnosis of gestational diabetes mellitus (GDM) who presented to Çukurova University Faculty of Medicine Hospital between 2024 and 2025, and to investigate the association between these parameters and pregnancy-related complications. Materials and Methods: This is a single-center, prospective study evaluating thyroid function tests in pregnant women diagnosed with GDM and the relationship between these tests and maternal and fetal complications. The study included third-trimester pregnant women who presented to the Endocrinology and Obstetrics outpatient clinics. Participants underwent one-step or two-step oral glucose tolerance testing (OGTT) between 24-28 weeks of gestation for GDM screening. Clinical history, family history, physical examination findings, and thyroid function test results of women with and without GDM were analyzed. All participants were followed until delivery, and data on delivery mode, gestational age at birth, and maternal and fetal complications were recorded. Biochemical parameters were obtained through the hospital's electronic medical record system (Mergen Tech EBYS) and by reviewing e-nabız data in patient files. Data analysis was conducted using IBM SPSS Statistics version 27.0. Results: Pregnant women with GDM had significantly higher body weight and body mass index (BMI) compared to those without GDM. A family history of diabetes and a history of GDM in previous pregnancies were more prevalent among GDM patients. No statistically significant differences were found between groups regarding age, height, education level, smoking status, employment status, socioeconomic level, presence of chronic diseases, hypertension, regular medication use, anti-thyroid peroxidase antibodies (Anti-TPO), anti-thyroglobulin antibodies (Anti-Tg), thyroid-stimulating hormone (TSH), free T4 (fT4), and free T3 (fT3) levels. Among maternal complications, polyhydramnios was observed in 6 women (15.0%) in the GDM group and was not observed in the non-GDM group, a statistically significant difference (p = 0.011). No significant differences were observed between the groups in terms of fetal and neonatal complications. A statistically significant negative correlation was found between TSH levels and preeclampsia in women with GDM (p = 0.039). A significant negative correlation was also found between maternal age and polyhydramnios in the GDM group (p = 0.038), suggesting a lower incidence of polyhydramnios with increasing maternal age. In the GDM group, there was a significant positive correlation between body weight and the incidence of preterm birth (p = 0.033), and preeclampsia (p = 0.041). Among non-GDM women, a significant negative correlation was found between maternal age and neonatal hyperbilirubinemia (p = 0.033). Additionally, in the non-GDM group, significant positive correlations were identified between smoking and preterm birth (p = 0.034), and between employment status and preterm birth (p = 0.034). In the non-GDM group, birth weight was significantly and negatively correlated with both preterm birth (p < 0.001) and cesarean delivery (p = 0.014), indicating that lower birth weight increased the likelihood of these outcomes. Conclusion: In our study, thyroid function tests were found to be similar in pregnant women with and without GDM. Among GDM patients, a negative correlation was found between TSH levels and preeclampsia, suggesting that higher TSH levels may be protective against preeclampsia. A higher BMI, excessive gestational weight gain, and a family history of diabetes were associated with a greater risk of GDM. Polyhydramnios was found to be significantly more common among GDM patients. In our study, lower birth weight was associated with an increased risk of preterm birth and cesarean delivery in the non-GDM group. Our findings emphasize the importance of evaluating thyroid function and associated risk factors during pregnancy as potential indicators of pregnancy-related complications. Keywords: Gestational diabetes mellitus, Thyroid-stimulating hormone, Anti-thyroid peroxidase antibody, Maternal complications, Fetal complications