Choice A rationale:
Large amount of bright red vaginal bleeding is the cardinal sign of placenta previa. This is because the placenta is abnormally positioned low in the uterus, covering the cervix partially or completely. When the cervix starts to dilate in preparation for labor, it can detach from the uterine wall, leading to significant bleeding. The blood is typically bright red, indicating fresh bleeding, and can be painless.
Severity of bleeding: The amount of bleeding can vary from spotting to massive hemorrhage, and it may start suddenly or gradually. Even a small amount of bleeding can be a sign of placenta previa and should not be ignored.
Risks of hemorrhage: Prompt recognition and management of bleeding are crucial to prevent potentially life-threatening hemorrhage for both the mother and the fetus.

Choice B rationale:
Severe pain with no bleeding is not a typical presentation of placenta previa. While some women with placenta previa may experience mild abdominal pain or cramping, severe pain without bleeding is more suggestive of placental abruption, a condition where the placenta prematurely separates from the uterine wall.

Choice C rationale:
High-grade fever is not a direct symptom of placenta previa. However, if a woman with placenta previa develops a fever, it could indicate an infection, which can further complicate the condition and require immediate medical attention.

Choice D rationale:
 Sudden sharp pain in the lower abdomen can be a sign of placental abruption but is not characteristic of placenta previa.