Final answer:
The nurse should first assess the client's fundus after noticing a soaked perineal pad with blood.
Step-by-step explanation:
In this scenario, the nurse caring for the client six hours after a vaginal delivery notices that the perineal pad is soaked with blood. The first action the nurse should take is to assess the client's fundus. The fundus is the upper part of the uterus, and assessing its firmness, position, and height can help determine if there is any uterine bleeding or abnormality. The nurse should also check the client's vital signs, including blood pressure (BP), but assessing the fundus takes priority in this situation.