Final answer:
The nurse should be most alert to changes in blood pressure and pulse as indicators of complications during and after childbirth.
Step-by-step explanation:
The nurse should be most alert to changes in blood pressure and pulse as these can be indicators of complications during and after childbirth. High blood pressure or an abnormal heart rate can indicate conditions such as preeclampsia or postpartum hemorrhage. Monitoring these vital signs closely can help the nurse identify potential problems and intervene promptly.