Final answer:
The nurse should monitor the fundal height after discovering a vulvar hematoma in a new mother postpartum, as this can be a sign of internal bleeding and possible postpartum hemorrhage.
Step-by-step explanation:
After notifying the health care provider that a new mother has a vulvar hematoma postpartum, the nurse's next action should be to monitor the fundal height. This is vital as changes in the fundal height can indicate whether there is increased bleeding inside the uterus. This could be a sign of internal bleeding which, given the new mother's symptoms of a drop in blood pressure and an elevated pulse, could suggest a postpartum hemorrhage complicating her recovery.