Objective: To characterize fetal spontaneous heart rate changes and movements and auditory-elicited heart rate changes in fetuses in diabetic pregnancies compared with those in uneventful, overweight pregnancies. Methods: Spontaneous heart rate and movements and maternal voice-elicited heart rate changes were observed in 46 mother-fetal pairs (n = 14 gestational diabetic and n = 32 overweight prepregnancy) at 36 (±1) weeks gestational age. Fetal heart rate changes, body movements, and breathing movements were observed for 20 minutes while the mother was at rest. Subsequently, each fetus was presented with a 2-minute audio recording of the mother's voice using the following 6-minute procedure: 2 minutes no-voice baseline, 2 minutes voice presentation, and 2 minutes no-voice postvoice period; heart rate was recorded continuously. Results: There were no differences in spontaneous heart rate changes, body movements, or breathing movements between the 2 groups. Fetuses in the overweight group showed an increase in the heart rate during the playing of their mother's voice, whereas fetuses in the diabetic group showed no response. Conclusions: Fetuses in overweight pregnancies responded to the mother's voice with an increase in the heart rate as has been reported previously in uneventful pregnancies. The lack of response to the mother's voice in fetuses in diabetic pregnancies may represent immature neural or auditory system development, an increased sensorineural threshold, and thyroid or iron deficiency.