**Core Concept**
Ectopic pregnancy is a life-threatening condition where the fertilized egg implants outside the uterus, often in the fallopian tube. Medical management aims to prevent tubal rupture and maintain a stable hemodynamic state. Key criteria for medical management include patient stability, low serum β-hCG levels, and absence of significant tubal rupture.

**Why the Correct Answer is Right**
The correct answer is **C. Pregnancy diameter <5 cm** because medical management of ectopic pregnancy is generally reserved for patients with a small ectopic mass (<3.5-4 cm) and low serum β-hCG levels. A pregnancy diameter of <5 cm is not a universally accepted criterion for medical management. In contrast, asymptomatic patients (A), serum β-hCG levels <2000 IU/L (B), and unruptured tubes (D) are all factors that may support medical management.

**Why Each Wrong Option is Incorrect**
**Option A:** Being asymptomatic does not exclude the possibility of tubal rupture, which is a life-threatening complication of ectopic pregnancy. Asymptomatic patients may still require surgical intervention.

**Option B:** A serum β-hCG level of <2000 IU/L is actually a criterion that supports medical management, not excludes it. Lower β-hCG levels are associated with a lower risk of tubal rupture.

**Option D:** An unruptured tube is not a criterion that excludes medical management. In fact, it is a desirable characteristic for medical management to be successful.

**Clinical Pearl / High-Yield Fact**
When managing ectopic pregnancy medically, it's essential to remember that the primary goal is to prevent tubal rupture and maintain hemodynamic stability. Serial β-hCG levels, ultrasound monitoring, and clinical assessment are crucial for guiding management.

**✓ Correct Answer: C. Pregnancy diameter <5 cm.**