Final answer:
The first action for the nurse to perform when the fetus displays occasional category 3 FHR patterns on the monitor during labor is to change the mother's position.
Step-by-step explanation:
The first action for the nurse to perform when the fetus displays occasional category 3 FHR patterns on the monitor during labor is to change the mother's position. This is because changing positions can help improve blood flow to the fetus and relieve any pressure that may be causing the abnormal FHR patterns. Administering oxygen to the mother is usually done if the FHR patterns do not improve after changing the position. Calling for a cesarean section or increasing the IV infusion rate would not be the first actions to perform in response to the FHR patterns.