ObjectiveTo test the hypothesis that, in diabetic pregnancies, left atrial shortening fraction (LASF) is decreased in fetuses with myocardial hypertrophy, compared to those without hypertrophy and to fetuses of non-diabetic mothers. MethodsFetal echocardiography was performed in women with pre-existing or gestational diabetes and in non-diabetic controls between 25 weeks’ gestation and term. LASF was calculated using the formula: (end-systolic diameter – end-diastolic diameter)/end-systolic diameter, and data were compared between diabetic women with and without fetal myocardial hypertrophy and controls. ResultsThe study population comprised 53 diabetic women and 45 controls. Out of the 53 fetuses of diabetic women, 14 had myocardial hypertrophy and 39 had normal septal thickness. Gestational age at the time of examination did not differ significantly between the control group and the two diabetic subgroups (P=0.57). Fetuses with myocardial hypertrophy presented a mean (±SD)LASFof0.32±0.11, those without myocardial hypertrophy 0.46±0.12, and those of normal mothers 0.53±0.09 (P<0.001). A significant inverse linear correlation was observed between LASF and septal thickness (r=−0.51,P<0.001). ConclusionsIn diabetic pregnancies, LASF is lower in fetuses with myocardial hypertrophy than it is in those without hypertrophy and in fetuses of non-diabetic women, suggesting that LASF could be a useful alternative parameter in the assessment of fetal diastolic function.