Is it safe to perform a computed tomography (CT) scan on a pregnant patient?

CT Scan Safety in Pregnancy

CT scanning is safe to perform on pregnant patients when clinically indicated, and imaging should never be delayed or withheld due to pregnancy concerns. 1

Radiation Exposure by Anatomic Region

The safety of CT in pregnancy depends critically on the anatomic region being scanned:

Head/Brain CT (Safest)

• Fetal radiation exposure from head CT is less than 0.01 mGy—essentially negligible and poses no measurable risk to the developing fetus. 1
• This represents approximately 1/5,000,000th of the established safety threshold and is 10,000 times lower than the threshold for any fetal harm. 1, 2
• Perform brain CT immediately when clinically indicated without delay. 1

Chest CT (Very Safe)

• Fetal exposure from chest CT is approximately 0.3 mGy, well below safety thresholds. 2
• For suspected pulmonary embolism, proceed with chest X-ray first, then CTA chest if needed, as fetal dose remains <0.3 mGy. 2

Abdomen/Pelvis CT (Requires Careful Consideration)

• CT abdomen/pelvis delivers 13-25 mGy to the fetus, which is higher but still generally safe. 3
• Cumulative ionizing radiation exposure should be kept as low as possible and below 50 mGy. 3
• Fetal doses below 50 mGy are not associated with detectable increases in adverse fetal outcomes including malformations, growth restriction, or fetal death. 1, 2

Clinical Decision-Making Algorithm

Step 1: Determine Clinical Urgency

• The primary consideration should be maternal benefit of accurate diagnosis, not fetal radiation exposure. 1, 2
• The risk of missing a potentially serious maternal diagnosis far outweighs the negligible radiation risk for most CT studies. 1

Step 2: Apply Imaging Hierarchy

1. First-line: Ultrasound without contrast for all abdominal/pelvic imaging when applicable. 3, 2
2. Second-line: MRI without gadolinium when ultrasound is inadequate. 3, 2
3. Third-line: CT with or without contrast when diagnosis cannot be made on ultrasound/MRI or when rapid diagnosis is essential. 2

Step 3: Proceed Based on Anatomic Region

• For head/neck/chest CT: Proceed immediately without delay when clinically indicated. 1, 2
• For abdomen/pelvis CT: Use only when ultrasound and MRI are inadequate or unavailable, and diagnostic information is essential. 3

Contrast Agent Considerations

Iodinated IV Contrast (Preferred if Contrast Needed)

• Modern non-ionic iodinated contrast has minimal theoretical risk of neonatal hypothyroidism. 1
• Use iodinated contrast only if absolutely required to obtain diagnostic information that would affect care of the fetus or mother. 3
• Less than 0.01% of CT contrast appears in breast milk, making breastfeeding safe after administration. 3, 2

Gadolinium-Based MRI Contrast (Contraindicated)

• Gadolinium is contraindicated in pregnancy. 3
• Gadolinium crosses the placenta and has been associated with increased risk of stillbirth, neonatal death, and rheumatologic conditions in offspring. 1, 2

Risk Thresholds and Safety Margins

• The threshold for significant risk of fetal damage is 100 mGy—far higher than typical diagnostic CT exposures. 1, 2
• Risk of malformations increases only with doses exceeding 150 mGy. 2
• Most diagnostic CT studies deliver well below 50 mGy to the fetus, even for abdomen/pelvis imaging. 3, 2

Patient Communication Framework

Reassure pregnant patients with these specific points:

• The fetal radiation exposure is 10,000 times lower than the threshold for any harm (for head CT). 1
• The benefit of accurate maternal diagnosis far outweighs the negligible risk. 1
• No adverse effects to the fetus are expected at diagnostic imaging exposure levels. 1

Common Pitfalls to Avoid

• Never delay clinically indicated head, neck, or chest CT due to pregnancy. 1
• Do not overestimate radiation risk—the risk of missing a serious maternal diagnosis is typically far greater than radiation risk. 1, 2
• Avoid gadolinium-based contrast as an alternative to iodinated CT contrast, as gadolinium carries greater fetal risk. 1, 2
• Document the clinical indication and risk-benefit assessment in the medical record. 2