Is a CT (Computed Tomography) scan of the brain safe for pregnant women?

CT Scan of the Brain in Pregnant Women

Brain CT is safe and should be performed without hesitation when clinically indicated in pregnant women, as the fetal radiation exposure is negligible (<0.01 mGy) and poses no measurable risk to the developing fetus. 1

Radiation Exposure and Safety Profile

The radiation dose to the fetus from a head CT is extraordinarily low and well below any threshold for concern:

• Head CT delivers less than 0.01 mGy to the fetus, which represents approximately 1/5,000,000th of the established safety threshold 2
• The maternal effective dose from head CT is approximately 2 mGy, which poses no meaningful cancer risk to the mother 1
• Fetal doses below 50 mGy are not associated with any detectable increases in adverse fetal outcomes, including malformations, growth restriction, or fetal death 1, 2
• The threshold for significant risk of fetal damage is 100 mGy—10,000 times higher than the actual exposure from head CT 1, 2

For context, chest CT delivers only 0.3 mGy to the fetus, and even abdominal/pelvic CT delivers 25-35 mGy—all still below the 50 mGy safety threshold 1, 2. Brain CT, being anatomically distant from the fetus, delivers far less radiation than any of these.

Clinical Decision-Making Framework

The primary consideration should be the maternal benefit of accurate diagnosis, not fetal radiation exposure, as the latter is negligible for head CT. 1

When evaluating a pregnant woman with acute neurological symptoms:

• Perform brain CT immediately when clinically indicated—do not delay or withhold imaging due to pregnancy 3, 4
• The risk of missing a potentially serious maternal diagnosis (stroke, hemorrhage, mass lesion) far outweighs the negligible radiation risk 2, 4
• Document the clinical indication and risk-benefit assessment in the medical record 1
• Delaying necessary imaging poses greater risk to both mother and fetus than the radiation exposure itself 2

Contrast Agent Considerations

If contrast-enhanced brain CT is required:

• Iodinated IV contrast appears safer than gadolinium-based MRI contrast for imaging in pregnancy 1
• Modern non-ionic iodinated contrast has minimal theoretical risk of neonatal hypothyroidism 1, 2
• Use iodinated contrast only if absolutely required to obtain diagnostic information that would affect care 1, 2
• Less than 0.01% of CT contrast appears in breast milk, making breastfeeding safe after administration 1, 2

Gadolinium-based MRI contrast should be avoided, as it crosses the placenta and has been associated with increased risk of stillbirth, neonatal death, and rheumatologic conditions in offspring 1, 2. This makes contrast-enhanced CT a safer option than contrast-enhanced MRI when contrast is necessary.

Alternative Imaging Modalities

While brain CT is safe, the general hierarchy for imaging in pregnancy is:

• Ultrasound first-line (when applicable for the clinical question) 1, 2
• MRI without gadolinium second-line when ultrasound is inadequate 1, 2
• CT with or without contrast when diagnosis cannot be made on ultrasound or MRI, or when rapid diagnosis is essential 1

However, for acute neurological emergencies (suspected stroke, intracranial hemorrhage, trauma), brain CT remains the most appropriate tool for initial rapid diagnosis and should not be withheld or delayed 4. MRI without gadolinium is generally considered safe in pregnancy and may be appropriate for non-urgent neurological evaluation 4, 5.

Common Pitfalls to Avoid

• Do not delay urgent brain CT due to exaggerated concern about radiation—the exposure is negligible and the maternal risk of delayed diagnosis is substantial 4
• Do not substitute gadolinium-enhanced MRI for contrast-enhanced CT if contrast is needed, as gadolinium poses greater theoretical risk 1
• Do not create unnecessary anxiety by overemphasizing minimal radiation exposure—counsel patients that brain CT delivers radiation equivalent to natural background exposure 2
• Do not perform imaging without documenting the indication and risk-benefit discussion in the medical record 1

Risk Communication

When counseling pregnant patients about brain CT:

• Reassure them that the fetal radiation exposure is 10,000 times lower than the threshold for any harm 1
• Explain that the benefit of accurate maternal diagnosis far outweighs the negligible risk 1, 2
• Emphasize that no adverse effects to the fetus are expected at these exposure levels 1, 2
• For comparison, the radiation from a brain CT is less than what the fetus receives from a few days of natural background radiation 2