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

Head CT During Pregnancy: Minimal Risk Profile

Head CT during pregnancy poses negligible risk to the fetus and should not be withheld when clinically indicated, as the fetal radiation exposure is minimal (<0.01 mGy) and far below any threshold for harm. 1, 2

Fetal Radiation Exposure from Head CT

• Head CT delivers essentially no measurable radiation dose to the fetus because the scanning beam is directed at the head, far from the uterus, and scatter radiation is negligible. 3
• The fetal dose from head CT is <0.01 mGy, which is orders of magnitude below any threshold for concern. 2
• For comparison, chest radiography (which is closer to the uterus) delivers <0.01 mGy, and even chest CT only delivers 0.3 mGy to the fetus. 4

Safety Thresholds and Risk Context

• 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, 5
• The threshold for significant risk of fetal damage is set at 100 mGy, with increased risks of mental retardation occurring only above this level (estimated at 0.025 IQ points lost per mGy above 100 mGy). 4
• Risk of malformations increases with doses exceeding 150 mGy, and 200-500 mGy has been suggested as a threshold that might warrant consideration of pregnancy termination. 4
• Head CT exposure is approximately 1/10,000th of these concerning thresholds, making it essentially risk-free from a radiation perspective. 2, 3

Clinical Decision-Making Algorithm

When head CT is clinically indicated in pregnancy:

1. Proceed without delay if there is suspicion of acute intracranial pathology (stroke, hemorrhage, trauma, mass lesion). 6
2. Do not substitute MRI solely to avoid radiation, as head CT delivers no meaningful fetal dose and MRI may delay diagnosis in acute settings. 6
3. No special precautions or shielding are required for head CT, as the fetus is not in or near the scanning field. 3
4. Document the clinical indication and risk-benefit assessment in the medical record. 4

Contrast Agent Considerations

• Iodinated IV contrast for head CT appears safe in pregnancy and should be used if clinically necessary for diagnosis. 1, 7, 8
• Modern non-ionic iodinated contrast agents have minimal risk, though theoretical concern for neonatal hypothyroidism exists and should be communicated to the pediatrician at birth. 1, 7, 8
• Iodinated contrast is safer than gadolinium-based MRI contrast, which crosses the placenta and has been associated with increased risk of stillbirth, neonatal death, and rheumatologic conditions in offspring. 4, 1, 8
• Less than 0.01% of CT contrast appears in breast milk, making breastfeeding safe immediately after administration. 1

Common Pitfalls to Avoid

• Do not delay or withhold head CT due to pregnancy when acute neurological pathology is suspected—the disease risk far exceeds any imaging risk. 4, 6
• Do not order MRI instead of head CT in acute settings simply because the patient is pregnant, as this delays diagnosis without providing meaningful safety benefit. 6
• Do not perform pregnancy testing before head CT unless there is clinical suspicion that the patient might have an ectopic pregnancy or other condition where pelvic imaging might be needed. 2
• Avoid exaggerated counseling about radiation risks that may cause unnecessary anxiety or lead to refusal of needed imaging—the actual risk is essentially zero. 5, 6

Maternal Risk Considerations

• The maternal effective dose from head CT is approximately 2 mGy, which is well within acceptable limits and poses no meaningful cancer risk. 4
• The primary consideration should be the maternal benefit of accurate diagnosis, not fetal radiation exposure, as the latter is negligible for head CT. 4, 6