Objective To evaluate the fetal cardiac function in gestational diabetes mellitus (GDM) pregnancies under different maternal glycemic controls.Methods Forty four GDM mothers received 78 fetal echocardiographic evaluations at three gestational periods (＜28,28-34 and ≥34 weeks) and were divided into poorly-(DM1) and well-(DM2)controlled groups according to their glycemic control at examination.Seventy uncomplicated mothers were selected as controls.Parameters of fetal cardiac anatomy and function were measured and analyzed.Results GDM fetuses' cardiac ventricular walls were thicker than controls',and the differences between DM1 and DM2 were not significant except for end-diastolic left ventricular walls.In both GDM groups,the aortic flow velocities increased earlier than pulmonary artery and DM1 fetuses changed earlier than DM2 ones.GDM fetuses' left atrial shortening fraction was smaller than the controls' in the period of ≥34 weeks and negatively correlated with thicknesses of left ventricular walls and interventricular septum in DM1 fetuses (r=-0.438 and -0.506).The right ventricular diastolic function in DM1 and DM2 fetuses decreased after the period of 28-34 weeks and in the period of ≥34 weeks respectively.Tei index of both left and right ventricles increased in DM1 group after the period of ＜28 weeks and in DM2 group only in the period of ≥34 weeks,with no significant differences between DM1 and DM2 groups in this period.Conclusion Fetuses of GDM mothers showed cardiac function impairments.Good maternal glycemic control may delay the impairments,but cannot reduce the degree.Some cardiac changes in GDM fetuses were similar to those in pregestational diabetic pregnancies except for several parameters and their changing time.