What is the most appropriate initial imaging study for a pregnant woman with severe abdominal pain, nausea, vomiting, and shortness of breath?

Abdominal Ultrasonography is the Most Appropriate Initial Imaging Study for a Pregnant Woman with Severe Abdominal Pain

Abdominal ultrasonography is the most appropriate initial imaging study for this 41-year-old pregnant woman at 19 weeks' gestation presenting with severe abdominal pain, nausea, vomiting, and shortness of breath.

Rationale for Ultrasonography as First-Line Imaging

The decision to use ultrasonography as the initial imaging modality is supported by multiple high-quality guidelines:

1. Safety in Pregnancy: Ultrasonography avoids ionizing radiation, making it the safest option for both mother and fetus 1.

2. Diagnostic Capability: Ultrasonography can effectively evaluate many common causes of abdominal pain in pregnancy, including:

   • Gallbladder pathology (given the right upper quadrant tenderness)
   • Hepatobiliary disease
   • Appendicitis (though less sensitive than CT)
   • Obstetric complications

3. Guideline Support: The Infectious Diseases Society of America (2024) specifically recommends "in pregnant people with suspected acute intra-abdominal abscess, US or MRI imaging can be considered as the initial diagnostic imaging modality" 1.

Clinical Considerations in This Case

The patient's presentation has several concerning features that guide our imaging approach:

• Right upper quadrant pain with epigastric tenderness: Suggests possible gallbladder disease, HELLP syndrome, or preeclampsia
• Hypertension history: Increases risk of preeclampsia-related complications
• Shortness of breath: Could indicate pulmonary complications or severe abdominal pathology
• 19 weeks' gestation: Second trimester, when physiological changes of pregnancy are significant but the uterus has not yet displaced abdominal organs extensively

Imaging Algorithm for Pregnant Women with Abdominal Pain

1. First-line imaging: Abdominal ultrasonography

   • Advantages: No radiation, readily available, can evaluate gallbladder, liver, kidneys, and fetus
   • Limitations: Operator-dependent, may have limited visualization due to body habitus or bowel gas

2. If ultrasonography is inconclusive:

   • MRI without contrast should be the next imaging study 1, 2
   • MRI provides excellent soft tissue contrast and can evaluate a wide range of pathologies without radiation

3. CT should be reserved for situations where diagnosis cannot be made with US or MRI and when the benefit outweighs the radiation risk 1.

Potential Diagnoses to Consider

Given the patient's presentation with right upper quadrant pain, epigastric tenderness, and hypertension history, several diagnoses should be considered:

• Acute cholecystitis: The ACR Appropriateness Criteria specifically recommends abdominal US as the initial diagnostic imaging modality for suspected acute cholecystitis 1.
• HELLP syndrome or preeclampsia: Given her hypertension history and current symptoms
• Acute fatty liver of pregnancy: Can present with right upper quadrant pain and vomiting
• Appendicitis: Though less likely with this pain distribution, it remains the most common surgical emergency in pregnancy 2

Common Pitfalls to Avoid

1. Delaying imaging due to pregnancy concerns: Modern ultrasonography has no known risks to the fetus and should not be delayed when clinically indicated.

2. Jumping directly to CT: Despite its superior diagnostic capability for many conditions, CT should not be the initial imaging choice in pregnancy due to radiation exposure.

3. Overlooking obstetric causes: While evaluating for general abdominal pathology, ensure that obstetric causes of pain are also assessed during ultrasonography.

4. Inadequate patient positioning: Proper positioning during ultrasonography is crucial to overcome the limitations imposed by the gravid uterus.

By following this evidence-based approach with ultrasonography as the initial imaging modality, clinicians can effectively diagnose the cause of this pregnant patient's abdominal pain while minimizing risk to both mother and fetus.