What are the guidelines for using computed tomography (CT) scans in obstetrics and gynecology?

Guidelines for CT Scan Use in Obstetrics and Gynecology

CT scans should be avoided in pregnancy whenever possible and should only be performed when the clinical benefit clearly outweighs the radiation risk, with non-ionizing imaging modalities like ultrasound and MRI being preferred alternatives. 1, 2

Radiation Risks and Safety Thresholds

• The threshold for significant risk of fetal damage is set at 100 mGy 1
• Fetal radiation exposure >50 mGy is associated with doubled risk of childhood cancer 2
• Exposure >100 mGy increases risk of mental retardation 2
• Exposure >150 mGy increases risk of malformations 2
• A single CT scan typically delivers radiation below these thresholds but still carries a minimal increased cancer risk 2

Appropriate Indications for CT in Obstetrics

During Pregnancy:

• CT should be performed only when strictly necessary 1
• Appropriate indications include:
  • Trauma assessment when maternal well-being is priority 2
  • Suspected intra-abdominal hemorrhage 2
  • When ultrasound findings are normal but symptoms persist 2
  • Suspected appendicitis (after inconclusive ultrasound) 2
  • Suspected pulmonary embolism (CT should be initial diagnostic imaging) 3
  • Suspected surgical complications 2

In Gynecology:

• CT has limited role in initial local staging of gynecological cancers due to poor soft tissue contrast 2
• CT is valuable for:
  • Detecting extrauterine metastases 2
  • Planning surgical approach 2
  • Evaluating treatment response 2
  • Surveillance for recurrence 2

Precautions When CT is Necessary

• Use proper abdominal shielding to minimize fetal exposure 1
• Consider CT as second choice to MRI 1
• Use low-dose protocols specifically designed for the indication 2
• Ensure cumulative ionizing radiation exposure is less than 50 mGy 1
• Obtain informed consent after discussing risks and benefits 2

Contrast Media Considerations

• Iodinated contrast should be used only when absolutely necessary 1
• There is limited trustworthy literature about safety of IV iodinated contrast in pregnancy 1
• Gadolinium-based contrast agents should be avoided during pregnancy as they cross the placenta 2
• Breastfeeding after iodinated contrast is considered safe (less than 0.01% of CT contrast present in breast milk) 1

Preferred Imaging Alternatives

• Ultrasound (without contrast) is the preferred initial imaging modality throughout pregnancy 1, 2

  • Limited Doppler study can be used but exposure time should be minimized 1

• MRI without gadolinium is preferred over CT imaging 1

  • Whole-body diffusion-weighted MRI (WB-DWI/MRI) can replace PET/CT for staging and tumor response evaluation 1
  • MRI provides excellent soft tissue contrast for pelvimetry and gynecologic conditions 2

Common Pitfalls to Avoid

• Failing to consider radiation exposure when imaging pregnant patients
• Using CT as first-line imaging when ultrasound or MRI would be sufficient
• Administering gadolinium contrast during pregnancy
• Not using proper abdominal shielding during necessary CT scans
• Performing multiple CT scans that could lead to cumulative radiation exposure exceeding safety thresholds

By following these guidelines, clinicians can make appropriate decisions about CT scan use in obstetrics and gynecology while minimizing risks to patients and fetuses.