A 19-year-old woman comes to the emergency room and reports that she fainted at work earlier in the day. She has mild vaginal bleeding. Her abdomen is diffusely tender and distended. In addition, she complains of shoulder and abdominal pain. Her temperature is 97.6degF, pulse rate is 120/min, and blood pressure is 96/50 mmHg. To confirm the diagnosis suggested by the available clinical data, the best diagnostic procedure is

**Core Concept**
The patient's symptoms, including abdominal tenderness, distension, shoulder pain, and vaginal bleeding, are suggestive of an ectopic pregnancy with possible rupture, leading to hemorrhagic shock. The clinical presentation is a classic example of the "triad of signs" associated with ectopic pregnancy: abdominal pain, vaginal bleeding, and shoulder pain due to irritation of the diaphragm by blood.

**Why the Correct Answer is Right**
The correct answer is an ultrasound examination, specifically a transvaginal ultrasound (TVUS), to confirm the diagnosis of an ectopic pregnancy. TVUS is the preferred imaging modality for evaluating the female pelvis, especially in cases of suspected ectopic pregnancy. It provides high-resolution images of the ovaries, fallopian tubes, and uterus, allowing for the detection of a pregnancy outside the uterine cavity.

**Why Each Wrong Option is Incorrect**
* **Option A:** Laparoscopy is an invasive procedure that may be required if the diagnosis is confirmed, but it is not the first-line diagnostic procedure.
* **Option B:** CT scan may be used in cases where ultrasound is inconclusive, but it is not the preferred initial imaging modality for suspected ectopic pregnancy due to radiation exposure.
* **Option D:** MRI is not typically used for the initial evaluation of suspected ectopic pregnancy due to its higher cost and limited availability.

**Clinical Pearl / High-Yield Fact**
In cases of suspected ectopic pregnancy, it is essential to maintain a high index of suspicion and perform a thorough physical examination, including a pelvic exam, to identify potential signs of rupture, such as abdominal tenderness and distension.

**Correct Answer:** C.

✓ Correct Answer: D. Culdocentesis