© This content is licensed under a Creative Commons Attributions 4.0 International License.Purpose: To investigate the effect of hemoglobin A1c level on central macular thickness and central, nasal, and temporal choroidal thickness in patients with gestational diabetes mellitus. Methods: This retrospective study included 41 patients who had been diagnosed with gestational diabetes mellitus and undergone a 75-g oral glucose tolerance test between 24 and 28 weeks of gestation. They were divided into two groups based on their hemoglobin A1c level (group 1: hemoglobin A1c <6.0% and group 2: hemoglobin A1c ≥6.0%). All patients underwent a complete ophthalmologic examination. The central macular thickness and central, nasal, and temporal choroidal thickness were measured using optical coherence tomography. Results: Of the 3,016 pregnant women screened, 7.5% (n=228) were diagnosed with gestational diabetes mellitus during the study period and 41 of these patients were included in the study. Group 1 comprised 48 eyes from 24 patients and Group 2 consisted of 34 eyes of 17 patients. The average body mass index values were 30.8 ± 3.3 and 35.1 ± 9.0, respectively (p=0.002). The insulin use rates were 29.2% and 76.5%, respectively (p=0.000). Mean central macular thickness values were 250.8 ± 14.3 μm and 260.9 ± 18.1 μm, respectively, and the difference was significant (p=0.008). Conclusions: Although the body mass index and central macular thickness values were significantly higher in Group 2, there was no difference in the central, nasal, and temporal choroidal thickness between the two groups.