What are the risks of getting a computed tomography (CT) scan during pregnancy?

Risks of CT Scan During Pregnancy

CT scans during pregnancy should be performed only when medically necessary, as they carry a small but real radiation risk to the fetus, though this risk is significantly below the threshold for causing fetal damage (100 mGy). 1

Radiation Risks to the Fetus

Quantifying the Risk

• The threshold for significant risk of fetal damage is set at 100 mGy 1
• A standard chest CT exposes the fetus to approximately 0.3 mGy 1
• Abdominal/pelvic CT exposes the fetus to higher radiation levels but still typically below harmful thresholds
• For comparison, a standard chest X-ray with proper shielding exposes the fetus to <0.01 mGy 1

Types of Potential Harm

1. Teratogenic effects:

   • Primarily a concern during organogenesis (first trimester)
   • Actual risk is much lower than commonly perceived by physicians 2
   • No increased risk of congenital malformations has been documented at diagnostic radiation doses

2. Carcinogenic effects:

   • Stochastic effect (no threshold dose)
   • Exposure >50 mGy is associated with doubled relative risk of childhood cancer 1
   • However, this translates to only 1.1-3 additional cancer cases per 1000 exposed children 1
   • The absolute risk remains very small

Guidelines for CT Use in Pregnancy

When CT May Be Indicated

• For diagnosis or exclusion of pulmonary embolism when other tests are insufficient 1
• For trauma evaluation when serious injury is suspected 3
• For certain oncological staging when MRI is unavailable 1
• When the benefit of diagnosis outweighs the small radiation risk

Risk Reduction Strategies

• Use abdominal shielding when possible 1
• Minimize fluoroscopy time and radiation dose 1
• Document radiation dose in medical records 1
• Consider low-dose CT protocols (1-3 mSv) when appropriate 1

Alternative Imaging Modalities

Preferred Non-Ionizing Options

1. Ultrasound:

   • First-line imaging modality for pregnant women
   • No known risks to the fetus
   • Limited by maternal body habitus and late-stage pregnancy (after 28-30 weeks) 1

2. MRI:

   • Safe alternative to CT, especially after first trimester 1
   • No ionizing radiation
   • Whole-body diffusion-weighted MRI can replace PET/CT for staging 1
   • Avoid gadolinium contrast as it crosses the placental barrier and has been associated with:
     • Increased risk of rheumatologic conditions in offspring
     • Increased risk of stillbirth or neonatal death 1

Clinical Decision Making

When considering CT during pregnancy:

1. Determine if the diagnostic information is necessary for maternal health
2. Consider if alternative non-ionizing imaging (ultrasound, MRI) can provide adequate information
3. If CT is necessary, use dose reduction techniques and proper shielding
4. Discuss risks and benefits with the patient, emphasizing that a single CT scan poses minimal risk to the fetus
5. Document the discussion and radiation dose in the medical record

Common Misconceptions

• Many physicians significantly overestimate the teratogenic risk of CT scans during pregnancy 2
• This misconception can lead to unnecessary anxiety and potentially harmful delays in maternal care
• In one study, 61% of family physicians estimated the risk of major malformations from abdominal CT to be ≥5% (actual risk is negligible at diagnostic doses) 2
• Some physicians even inappropriately recommended abortion after CT exposure 2

Remember that maternal health is paramount, and necessary imaging should not be withheld when indicated, as the risk to the mother from delayed diagnosis often far exceeds the small radiation risk to the fetus.