Final answer:
The most critical information for the nurse is the reason for the previous cesarean delivery to inform current labor and delivery management and assess VBAC safety.
Step-by-step explanation:
The most critical information the nurse must obtain at this point is d) The reason for the previous cesarean delivery. This is crucial because the reason for the prior cesarean may affect the current labor and delivery approach. Certain conditions, like placenta previa or uterine rupture, that necessitated the previous cesarean might recur or influence the management of the present delivery. Additionally, understanding the previous rationale can help assess the safety of attempting a vaginal birth after cesarean (VBAC).
Present pregnancy complications, allergies to medications, and past medical history are also important but knowing the specific reason for the previous C-section is immediately relevant to the delivery strategy.