Is it safe for a pregnant patient to undergo a computed tomography (CT) scan?

CT Scan Safety in Pregnancy

CT scanning is generally safe during pregnancy when clinically indicated, with the critical distinction being whether the fetus is directly in the scanning field—head and chest CT deliver negligible fetal radiation (<0.01 mGy), while abdominopelvic CT delivers 13-25 mGy, both well below the 50-100 mGy safety threshold. 1

Radiation Exposure by Anatomic Region

Scans Outside the Abdomen/Pelvis (Minimal Risk)

• Head CT delivers less than 0.01 mGy to the fetus—approximately 1/5,000,000th of the established safety threshold and poses no measurable risk to the developing fetus 2
• Chest CT delivers approximately 0.3 mGy to the fetus, which is negligible and does not require special consideration in the risk-benefit analysis 3
• These examinations should not be delayed or withheld due to pregnancy when clinically indicated 2

Abdominopelvic CT (Higher but Still Safe Exposure)

• Abdominopelvic CT delivers 13-25 mGy to the fetus, which requires consideration but remains well below safety thresholds 1
• Cumulative radiation exposure should be kept below 50 mGy across all imaging studies during pregnancy 1

Safety Thresholds and Fetal Risk

The established safety framework has three key thresholds:

• Below 50 mGy: No detectable increase in adverse fetal outcomes including malformations, growth restriction, or fetal death 1, 3
• 100 mGy: Threshold for significant risk of fetal damage—10,000 times higher than head CT exposure 2, 3
• Above 150 mGy: Risk of malformations begins to increase 3

Clinical Decision-Making Algorithm

Step 1: Determine Anatomic Region

• If head or chest CT: Proceed immediately when clinically indicated—fetal radiation is negligible and should not factor into the decision 2, 4
• If abdominopelvic CT: Consider alternative imaging first, but do not withhold if clinically necessary 1

Step 2: Consider Imaging Alternatives (for abdominopelvic studies)

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

Step 3: Proceed with CT When Indicated

• The primary consideration is maternal benefit of accurate diagnosis, not fetal radiation exposure 2, 3
• The risk of missing a serious maternal diagnosis far outweighs the negligible radiation risk 2
• Document the clinical indication and risk-benefit assessment in the medical record 3

Contrast Agent Considerations

Iodinated Contrast (for CT)

• Not an absolute contraindication in pregnancy, but use only if absolutely required to obtain diagnostic information affecting maternal or fetal care 1
• Modern non-ionic iodinated contrast has minimal theoretical risk of neonatal hypothyroidism 1, 2
• Less than 0.01% appears in breast milk, making breastfeeding safe after administration 1

Gadolinium (for MRI)

• Gadolinium is contraindicated in pregnancy—it crosses the placenta and has been associated with increased risk of stillbirth, neonatal death, and rheumatologic conditions in offspring 1, 2, 3
• Iodinated CT contrast is safer than gadolinium-based MRI contrast when contrast-enhanced imaging is necessary 2, 3

Patient Communication Framework

Reassure patients with specific data:

• For head/chest CT: Fetal exposure is 10,000 times lower than the threshold for any harm 2
• For abdominopelvic CT: Exposure remains 2-4 times below the safety threshold where no adverse effects are expected 1
• No adverse effects to the fetus are expected at these exposure levels 2
• The benefit of accurate maternal diagnosis far outweighs the negligible risk 2

Common Pitfalls to Avoid

• Do not delay or withhold head or chest CT due to pregnancy—the fetal radiation is negligible and the maternal diagnostic benefit is paramount 2, 4
• Do not use gadolinium-based MRI contrast as an alternative to iodinated CT contrast—gadolinium has documented fetal risks while iodinated contrast does not 2, 3
• Do not advise stopping breastfeeding after CT with iodinated contrast—less than 0.01% appears in breast milk 1
• Do not perform CT without documenting the clinical indication when the abdomen/pelvis is involved 3