Final answer:
The priority action during the fourth stage of labor is monitoring the mother's vital signs and the fundal height to ensure her well-being and to prevent postpartum complications like hemorrhage.
Step-by-step explanation:
The priority action during the fourth stage of labor or recovery stage is B) Monitoring vital signs and fundal height. This stage focuses on ensuring the well-being of the mother after the birth of the baby, including inspecting the expelled placenta and fetal membranes for completeness and monitoring uterine contractions as the uterus begins involution to return to its pre-pregnancy size.
Monitoring includes observing for signs of postpartum hemorrhage and confirming that the uterus is contracting well to minimize blood loss. While administering pain medication, encouraging ambulation, and initiating breastfeeding are also important, they are not the priority actions at this stage.