Radiation Exposure and Safety in Head CT During Pregnancy

Fetal Radiation Exposure and Risk Thresholds

The European Society of Cardiology notes that chest radiography and chest CT deliver less than 0.01 mGy and 0.3 mGy to the fetus, respectively, for comparison with head CT doses 1
Fetal doses below 50 mGy are not associated with detectable increases in adverse fetal outcomes, including malformations, growth restriction, or fetal death, according to the American Society of Anesthesiologists 2, 3, 4
The threshold for significant risk of fetal damage is set at 100 mGy, with increased risks of mental retardation occurring only above this level, as stated by the American Society of Anesthesiologists 2, 3, 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, according to the American Society of Anesthesiologists 2, 3, 4

The American Heart Association recommends documenting the clinical indication and risk-benefit assessment in the medical record when head CT is clinically indicated in pregnancy 1, 3, 4
Iodinated IV contrast for head CT appears 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, as noted by the European Society for Medical Oncology 5

The American Thoracic Society states that the maternal effective dose from head CT is approximately 2 mGy, which is well within acceptable limits and poses no meaningful cancer risk 6
The primary consideration should be the maternal benefit of accurate diagnosis, not fetal radiation exposure, as the latter is negligible for head CT, according to the American Society of Anesthesiologists 3, 4

The American College of Radiology recommends ultrasound without contrast as the first-line imaging modality throughout pregnancy, due to its safety and effectiveness in providing diagnostic information 7, 8
The American College of Radiology suggests MRI without gadolinium as the second-line imaging modality when ultrasound is inadequate, as it provides detailed images without the use of ionizing radiation 7, 8, 9
CT imaging with or without contrast should be reserved for problematic situations where diagnosis cannot be made on ultrasound or MRI, and the diagnostic information is essential for the care of the fetus or mother 10, 11, 12, 13

The American College of Radiology recommends keeping cumulative ionizing radiation exposure below 50 mGy to minimize the risk of radiation-induced harm to the fetus 7, 8
The use of low-dose CT protocols is recommended when CT is required, to minimize radiation exposure to the fetus 10, 11, 12, 13
The American College of Radiology states that modern non-ionic iodinated contrast has no effect on the thyroid gland, but potential risk of neonatal hypothyroidism exists theoretically, although it is minimal with current agents 7, 8

The American College of Radiology recommends using iodinated contrast only if absolutely required to obtain diagnostic information that would affect the care of the fetus or mother 7, 8
Less than 0.01% of CT contrast appears in breast milk, making breastfeeding safe after administration 7, 8
Gadolinium-based MRI contrast is not recommended as an alternative to iodinated CT contrast, as it crosses the placenta and has been associated with increased risk of stillbirth, neonatal death, and rheumatologic conditions in offspring 14, 9

The American College of Radiology recommends confirming fetal gestational age first, then proceeding with standard imaging protocol using appropriate radiation safety measures, as diagnostic X-rays outside the abdomen/pelvis pose negligible fetal risk (<1 mGy) and should not be deferred when clinically indicated 15
For extremity and cervical spine radiographs, the American College of Radiology suggests proceeding with standard imaging protocol as these expose the fetus to minimal radiation (<10 mGy), well below the 50 mGy safety threshold 15
Women can be reassured that the benefit far outweighs the risk for diagnostic imaging when radiographs and CT scans do not involve the abdomen or pelvis, as the predicted fetal absorbed dose is less than 1 mGy 15

Pelvis radiograph has an approximately 1.1 mGy fetal dose, according to the American College of Radiology 15
Pelvis CT has an approximately 25-35 mGy fetal dose, as reported by the American College of Radiology 15
For suspected appendicitis in the first trimester, the American College of Radiology and the Infectious Diseases Society of America recommend performing pregnancy testing prior to imaging, then using ultrasound or MRI instead of CT 16, 17

For pregnant patients with suspected pulmonary embolism, the American College of Radiology recommends performing a chest X-ray first, then proceeding to CTA chest if needed, as the fetal dose remains <0.3 mGy 18