Final answer:
The most concerning result during a non-stress test is when, after 40 minutes of monitoring, the FHR is unchanged and the fetus is nonreactive to stimulation, which could indicate fetal distress and require emergency birth.
Step-by-step explanation:
The result that causes the greatest concern during a non-stress test for fetal heart rate (FHR) monitoring is C. After 40 minutes of monitoring, the FHR is unchanged and the fetus is nonreactive to stimulation. This could indicate fetal distress, which is associated with a sustained decrease or increase in the FHR. A lack of reactivity can be a sign that there is a problem with oxygenated blood flow being restored to the fetus following contractions. In such cases, emergency birth via vacuum, forceps, or a Caesarian section might be necessary to ensure the safety of the fetus.
In contrast, an acceleration of the FHR in response to fetal movement (Option A) is a normal, expected finding and indicates fetal well-being. Similarly, fetal movement after stimulation (Option B) and intermittent accelerated FHR with fetal movement (Option D) are also normal responses during a non-stress test. These results suggest the fetus is healthy and responding appropriately to stimuli.