The Impact of Thyroid Dysfunction on The Development of Gestational Diabetes Mellitus and Pregnancy Outcomes: An Observational Cohort Study

Abstract

Background: Gestational Diabetes Mellitus(GDM) and thyroid dysfunction (TD) are the two most prevalent endocrinopathies during pregnancy.

Methods: The observational cross-sectional study was conducted in an outpatient clinic from May 2024 to May 2025. 72 patients with GDM (study group) and 40 volunteers (control group) were selected to participate in the study. Anthropometric data (body mass – BM, body mass index – BMI) and an oral glucose tolerance test were carried out for all participants during all three trimesters of pregnancy. Thyroid function (thyroid-stimulating hormone – TSH, thyroid antibodies) was assessed in the first trimester of pregnancy. A special structured questionnaire was developed for socio-economic and anamnesis data. Odds ratio (OR) and 95% Confidence intervals (95%CI) were assessed for factorial analysis.

Results: DM in the first trimester was manifested in 13 patients (18.1%), in the second trimester – in 42 patients (58.3%), in the third trimester – in 17 patients (23.6%). The presence of TD was a significant factor for GDM – the TD was revealed in 55 patients (76.4%) of the study group and 26 patients (54.2%) of the control group – OR = 2.74, 95%CI – 1.25-6.01, p=0.012. The percentage of patients with TSH more than 4 mcU/l was significantly higher in the study group compared to the control group (38.8% vs. 18.8%; OR=2.76, 95%CI – 1.16-6.56, p=0.022). It should also be noted that GDM in patients with TD was manifested significantly earlier than in patients without TD – 19.6±6.2 weeks vs. 24.8±4.4 weeks, t-test=3.21, p=0.002. Body mass gain at the end of the third trimester was also significantly higher in GD patients with TD compared to GDM patients without TD – 14.4±2.5 kg vs. 12.6±2.1 kg, t-test=2.69, p=0.009. The pregnancy in 30 patients (41.7%) with TD in the study group was achieved through IVF; IVF was used in 24 cases with TD (50.0%) in the control group. The difference was not significant. Therefore, the combination of IVF and TD cannot be considered a risk factor for GDM.

Conclusion: TD may be considered a noteworthy factor in the development of GDM. GDM may manifest earlier, and the patient’s body mass gain may be higher if TD is present during pregnancy. The combination of IVF and TD cannot be considered a risk factor for GDM.