Final answer:
The priority nursing action upon detecting a fetal heart rate of 174 beats/minute at 38 weeks' gestation is to notify the health care provider due to the possibility of fetal distress indicated by tachycardia.
Step-by-step explanation:
The appropriate nursing action when assessing a fetal heart rate (FHR) of 174 beats/minute at 38 weeks' gestation is to notify the health care provider (HCP). This is considered a priority action because the normal FHR range is approximately 110-160 beats per minute, and a rate of 174 beats/minute may suggest tachycardia, which could indicate fetal distress or another complication. It is also important to distinguish between the fetal heart rate and the maternal heart rate, hence checking the mother's heart rate could be a subsequent action to ensure the rate obtained is not the mother's. Documenting the finding and informing the client about the fetal heart rate's significance may follow after communication with the HCP.