Final answer:
The precepting nurse would intervene if the new nurse attempted vibroacoustic stimulation during fetal bradycardia, as this could indicate fetal distress and worsen the condition.
Step-by-step explanation:
If a new nurse is preparing to assess the fetal heart rate response to stimulation with vibroacoustic stimulation, the action that would prompt the precepting nurse to intervene is if the nurse attempts stimulation in the presence of fetal bradycardia. The reason for this is that vibroacoustic stimulation should not be performed when there is an existing abnormal fetal heart rate pattern such as bradycardia. Bradycardia could indicate fetal distress, and further stimulation could worsen the condition. Therefore, it is advised to only perform vibroacoustic stimulation when the fetal heart rate is at a normal baseline and there are no signs of fetal distress.