OBJECTIVES In mothers with pre-gestational or gestational diabetes, abnormal arterial stiffness (stiffer arteries) has been reported. The impact of abnormal maternal arterial stiffness on fetal placental and cardiovascular physiology is unknown. The purpose of the study was to determine the impact of maternal diabetes on maternal arterial stiffness and the association with fetal cardiovascular physiology as measured by fetal echocardiography. METHODS Between December 2013 and January 2017 we conducted a prospective study on diabetic (otherwise healthy) and non-diabetic, healthy pregnant mothers (at 20-28 gestational weeks and 18-40 years of age) who had a normal fetal cardiac echocardiogram and obstetric ultrasound. Clinical data were collected by means of a patient questionnaire, measurement of blood pressure, height and weight, arterial augmentation index and fetal placental and cardiovascular parameters by fetal echocardiography. Descriptive statistics were calculated. Comparisons were made using parametric and non-parametric tests between controls and diabetic mothers. RESULTS Twenty-three healthy pregnant controls and 43 diabetic pregnant women (n = 22 pre-gestational, n = 21 gestational) were included in the study. Maternal arterial augmentation index was higher in those with diabetes compared to healthy controls (12.4 ± 10.6% versus 4.6 ± 7.9%; p = 0.003). Fetal aortic valve velocity time integral was higher in fetuses whose mothers had diabetes compared to non-diabetic mothers (7.7 ± 1.9 cm versus 6.3 ± 2.9 cm; p = 0.022). Left ventricular myocardial performance index was lower in diabetic pregnancies compared to controls (0.40 ± 0.09 versus; 0.46 ± 0.11 p = 0.02). Umbilical artery resistance index was lower in diabetic pregnancies with hemoglobin A1C levels ≥6.5% compared to those with HbA1c levels <6.5 (HbA1c ≥6.5%: 0.69 ± 0.06, n = 15 versus HbA1c <6.5%: 0.76 ± 0.08, n = 21; p = 0.009) but not at higher HbA1C cut-offs. A correlation between arterial augmentation index and velocity time integral, myocardial performance index or umbilical artery resistance index was not found. CONCLUSION Arterial stiffness is higher in pregnant women with diabetes compared to controls. Fetuses of diabetic mothers show altered cardiovascular parameters with higher velocity time integral and lower left ventricular myocardial performance index, markers of myocardial function. Placental function assessed by umbilical artery resistance was normal despite differences between groups. Arterial stiffness did not correlate with placental or fetal cardiovascular variables. Instead, the findings likely represent a shared response to the environment of abnormal glucose metabolism. The clinical significance of these findings is yet to be determined.