Final answer:
The nurse should be most concerned about a client with persistent, severe abdominal pain and vaginal bleeding.
Step-by-step explanation:
The client of most concern to the nurse is Option C: A client with persistent, severe abdominal pain and vaginal bleeding. Severe abdominal pain and vaginal bleeding during pregnancy can indicate a serious complication such as placental abruption or ectopic pregnancy. These conditions require immediate medical attention as they can be life-threatening for both the mother and the baby.
Option A: A client experiencing mild swelling in the ankles is a common symptom in pregnancy called edema and is typically not a cause for concern unless accompanied by other symptoms.
Option B: Occasional heartburn after meals is a common discomfort during pregnancy and does not pose a significant threat to the client and the baby.
Option D: Expressing concern about weight gain is a common concern for many pregnant clients and does not indicate an immediate health risk.