Final answer:
A nurse should report persistent fetal bradycardia below 100 bpm during a vacuum extraction birth, as it could indicate fetal distress requiring immediate medical intervention. Option a is the answer.
Step-by-step explanation:
While assisting with a vacuum extraction birth, a nurse should immediately report to the physician if there is persistent fetal bradycardia below 100 bpm. This is of concern because each contraction sharply reduces oxygenated blood flow to the fetus, making it critical that a period of relaxation occurs after each contraction to restore oxygenation. Fetal distress, such as sustained heart rate decreases, can result from contractions that are too intense or prolonged, leading to inadequate oxygen supply and requiring an emergency intervention, which could include the use of a vacuum, forceps, or a Caesarian section.