Evaluation of the Relationship Between 1st Trimester HbA1C, Fasting Blood Glucose, Thyroid Function Tests and Gestational Diabetes Mellitus

Objective: This study aimed to examine the relationship between gestational diabetes mellitus (GDM) and fasting blood glucose (FBG), thyroid function tests, and HbA1C values in the first trimester of healthy pregnant women who do not have DM and visit our gynecology and obstetrics polyclinic for regular checkups. Methods: This retrospective study included pregnant patients who applied to the Karaman Training and Research Hospital, Clinic of Obstetrics and Gynecology between 01.08.2023 and 01.05.2024. The department applied statistical analyses using the Statistical Package for the Social Sciences (SPSS Inc., version 20.0; Chicago, IL). Statistical significance was set as p<0.05. Results: Our study included 78 patients: 59 (75.6%) were in the non-GDM group and 19 (24.4%) were in the GDM group. We calculated the under the curve as 0.912 (0.60-0.96) for 2nd trimester FBG at a cut-off value of 88 and 0.786 (0.37-0.93) for 2nd trimester HbA1C at a cut-off value of 5. We observed that both 2nd trimester FBG and 2nd trimester HbA1C significantly outperformed 1st-trimester FBG in predicting GDM (p=0.00, p=0.04). It was observed that 2nd-trimester FBG predicted GDM significantly betterthan 2nd-trimester HbA1C (p=0.028). Although no statistically significant difference was detected between 1st trimester HbA1C and 2nd trimester HbA1C in predicting GDM (p=0.481), it was observed that 2nd trimester FBG predicted GDM statistically significantly betterthan first trimester HbA1c (p=0.004). Conclusion: First- and second-trimester HbA1c and FBG and oral glucose tolerance test (OGTT) values can predict gestational diabetes. HbA1C cannot be used instead of OGTT, but it is an important predictor.