OBJECTIVE: To investigate the morphology of the corpus callosum (CC) in fetuses of pregnant women with diabetes. MATERIALS AND METHODS: This prospective study was conducted between February 2024 and August 2024 at a tertiary hospital and included a total of 81 pregnant women, divided into three groups: 27 with gestational diabetes (GDM), 27 with pregestational diabetes (PGDM), and 27 controls. For each patient, CC and cavum septum pellucidum (CSP) measurements, tela-choroidea-to-anterior-cerebral-artery distance (TACAD), and Doppler parameters of the anterior cerebral artery were examined. RESULTS: The mean CC length significantly differed among the three groups (p = 0.00). Post hoc Tukey analysis showed a significant difference between the control group and the PGDM group (p = 0.001), as well as between the control group and the GDM group (p = 0.002). No significant differences were found among the three groups in terms of CC width, TACAD, anterior cerebral artery Doppler parameters, or CSP width and length (p >
0.05). The CC/head circumference ratio was significantly different among the three groups (p = 0.000). CONCLUSION: We found that fetal CC morphology was affected in pregnancies presenting with GDM and PGDM, likely due to increased transplacental transfer of nutrients caused by maternal hyperglycemia, which accelerates fetal growth.