## **Core Concept**
The clinical scenario describes a pregnant woman with mild lower abdominal pain and an empty uterine cavity on transvaginal ultrasound (TVS), with a serum beta-human chorionic gonadotropin (β-hCG) level of 700 IU/L. This presentation suggests an **ectopic pregnancy**, a condition where the embryo implants outside the uterine cavity, most commonly in the fallopian tubes.

## **Why the Correct Answer is Right**
The correct approach in this scenario, given the suspicion of an ectopic pregnancy, is to **repeat the β-hCG level and perform a repeat TVS**. This is because a β-hCG level of 700 IU/L is considered low for an intrauterine pregnancy that should be visible on TVS (typically, a gestational sac should be visible with a β-hCG level around 1000-2000 IU/L). The discriminatory zone, where an intrauterine pregnancy should be visible on TVS, varies but is generally around 1000-2000 IU/L. Given the empty uterine cavity and the patient's symptoms, it's crucial to monitor the β-hCG level to ensure it's rising appropriately (as expected in a normal pregnancy) or to confirm a plateau or drop, which could indicate an ectopic pregnancy.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Immediate surgical intervention without further diagnosis could be premature without confirming the diagnosis of an ectopic pregnancy through imaging or failed medical management.
- **Option B:** Administering methotrexate immediately might be appropriate for a confirmed ectopic pregnancy under certain criteria, but more information (like the size of the ectopic mass, if visible) and a definitive diagnosis are needed first.
- **Option C:** Expectant management would be inappropriate given the clinical presentation suggestive of an ectopic pregnancy, which requires prompt intervention to prevent rupture and severe complications.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is the **discriminatory β-hCG level**, which is the level above which an intrauterine pregnancy should be visible on TVS. This value can vary slightly by institution and ultrasound equipment but is generally around 1000-2000 IU/L. This concept is critical in the evaluation of early pregnancy complications, especially when suspecting an ectopic pregnancy.

## **Correct Answer:** B. Repeat β-hCG and TVS.