Final answer:
The combination of a positive pregnancy test with hypovolemia and peritoneal signs most likely indicates an ectopic pregnancy, which is a serious medical emergency requiring immediate attention.
Step-by-step explanation:
A positive pregnancy test combined with signs of hypovolemia (such as tachycardia and hypotension) and peritoneal signs (rebound, guarding, and severe abdominal tenderness) suggests a medical emergency. In the context of a recently discovered pregnancy, the most likely diagnosis is A. Ectopic pregnancy. An ectopic pregnancy occurs when a fertilized egg implants outside of the uterus, typically in the fallopian tube, but can also occur in places like the ovary or abdominal cavity. This can lead to life-threatening bleeding, and symptoms include abdominal pain, hypovolemia, and shock. Immediate medical intervention is crucial for the health of the patient.