Gestational diabetes mellitus (GDM) incidence can increase up to 14%. GDM creates a risk for developing type 2 diabetes mellitus after pregnancy. Umbilical artery (UA) and fetal middle cerebral artery (MCA) changes in GDM have been studied before. The previous studies have contradictory results. In the current study, we aim to detect and define the impairment of color Doppler ultrasound (CDUS) characteristics in UA and MCA for the pregnant with GDM. Methods: US examinations were all performed at 18–22 weeks of gestation with a 3.5 MHz convex transducer. We recorded peak systolic velocity (PSV), end diastolic velocity, pulsatility index, resistive index, and systole/diastole ratio values of both UA and MCA at 18–22 weeks of gestation. GDM diagnosis was created according to the American Diabetes Association guidelines. Results: Sixty GDM patients and 61 healthy controls were included into the study. Median MCA PSV value was lower in GDM group (28 cm/s vs. 32 cm/s, P = 0.37). Among UA CDUS parameters, we cannot find any significant difference. In GDM group, we could not detect any significant correlation between CDUS parameters and HbA1C values. Conclusion: GDM changes fetal brain hemodynamics and the change can be detected at 18–22 weeks of gestation. Decreased fetal MCA PSV values can serve as an early warning for GDM.