Final answer:
The most accurate method for a nurse to determine that fetal heart sounds are heard is by performing Leopold's maneuvers before using a Doppler ultrasound device to locate the fetus and identify the best area for auscultation.
Step-by-step explanation:
The nurse most accurately determines that the fetal heart sounds are heard by performing Leopold's maneuvers first to determine the location of the fetal heart. This technique allows the nurse to identify the position of the fetus in the womb and hence, the optimal location on the mother's abdomen to place the Doppler ultrasound device for auscultation.
It is important to note that while the fetal heart rate can be greater than 140 BPM, this alone does not confirm accurate detection of the fetal heart sound. Also, it is essential to differentiate between maternal and fetal heart rates, and that's where palpating the maternal radial pulse while listening to the fetal heart rate ensures the sounds are not confused.