What is the evidence for using Computed Tomography (CT) scans in pregnant women?

CT Imaging in Pregnant Women: Evidence and Guidelines

CT scans should be reserved for problematic situations in pregnant women when a diagnosis cannot be made using ultrasound or MRI, and when performed, low-dose CT protocols should be used. 1

Primary Imaging Modalities in Pregnancy

First-Line Options

• Ultrasound:

  • First-line imaging modality for most conditions in pregnancy 1, 2
  • Nearly 100% sensitive for detecting large stones (>5mm) and hydronephrosis 1
  • Color Doppler increases sensitivity for detection of conditions like acute pyelonephritis 1
  • No ionizing radiation exposure to mother or fetus

• MRI without gadolinium:

  • Preferred second-line option when ultrasound is inadequate 1, 2
  • Excellent soft tissue contrast without ionizing radiation 2
  • Can detect conditions like pyelonephritis, renal abscesses, hydronephrosis, and pyonephrosis 1
  • Diffusion-weighted imaging (DWI) can be useful in diagnosing various conditions 1

CT Imaging in Pregnancy: Risks and Appropriate Use

Radiation Risk Considerations

• Fetal radiation exposure below 50 mGy is not associated with detectable increases in adverse fetal outcomes 2
• Typical fetal doses from common CT procedures:
  • CT abdomen/pelvis: 13-25 mGy
  • CT chest: 0.3 mGy 2

Appropriate Indications for CT in Pregnancy

CT should be used only when:

1. Diagnosis cannot be made using ultrasound or MRI 1
2. The clinical benefit outweighs the potential radiation risk 2, 3
3. In emergency situations such as:
   • Suspected intra-abdominal hemorrhage
   • Unstable pelvic fractures
   • Suspected pulmonary embolism (CT should be first-line) 2
   • Trauma with suspected serious injury 4

Risk Mitigation Strategies

When CT is necessary during pregnancy:

• Use low-dose CT protocols 1
• Limit scan range to the area of interest 2
• Use proper abdominal shielding when appropriate 2
• Follow ALARA principle (As Low As Reasonably Achievable) 2

Contrast Agent Considerations

Iodinated Contrast (CT)

• Should be used only when absolutely necessary 2
• Limited literature about safety, but appears relatively safe 2, 5
• Use with caution due to risk of fetal hypothyroidism 5

Gadolinium Contrast (MRI)

• Contraindicated during pregnancy 2
• Crosses the placenta and accumulates in amniotic fluid and fetal tissue 2, 3
• Should only be used if the potential benefits justify the unknown risks to the fetus 1

Special Clinical Scenarios

Suspected Acute Appendicitis

• Ultrasound is initial modality of choice
• If ultrasound is negative, MRI or CT can be obtained 4

Suspected Pulmonary Embolism

• CT should be the initial diagnostic imaging modality 4

Suspected Renal Colic/Hydronephrosis

• Ultrasound should be initial study of choice 1, 4
• CT only if diagnosis remains unclear after ultrasound and MRI 1

Trauma

• Ultrasound can be initial imaging evaluation
• CT should be performed if serious injury is suspected 4

Patient Communication

When discussing CT imaging with pregnant patients:

• Explain that the benefit of proper diagnosis typically outweighs the minimal risk when clinically indicated 2
• Provide concrete information about radiation doses to alleviate anxiety 2
• Emphasize that most diagnostic imaging procedures deliver doses well below thresholds of concern 2

CT imaging in pregnant women carries some risk but can be invaluable when used appropriately. The decision to perform CT should be based on careful consideration of the clinical necessity, with ultrasound and MRI preferred as initial imaging modalities when feasible.