Is it safe to have a computed tomography (CT) scan during pregnancy?

Safety of CT Scans During Pregnancy

MRI without contrast and ultrasound are preferred over CT scans during pregnancy whenever possible, but CT can be performed when medically necessary if the benefits outweigh the risks. 1, 2

Radiation Risks to the Fetus

• The threshold for significant risk of fetal damage is set at 100 mGy of radiation exposure 1
• Fetal radiation doses below 50 mGy are considered acceptable with minimal risk to the fetus 1
• A single CT procedure is unlikely to result in exposure exceeding 50 mGy 1
• Radiation exposure >100 mGy is associated with increased risk of mental retardation (estimated at 0.025 IQ point loss per mGy above 100 mGy) 1
• Risk of childhood cancer is theoretically doubled with fetal radiation >50 mGy, but the absolute risk remains extremely low (estimated increase of 1.1 to 3 per 1000) 1

Fetal Radiation Exposure by CT Type

• CT abdomen/pelvis (no contrast): 13-25 mGy fetal dose 1
• Chest CT: 0.3 mGy fetal dose 1
• Chest radiograph (two views): 0.0005-0.01 mGy fetal dose 1
• CT scans where the fetus is not directly in the imaging field (e.g., head or chest CT) result in minimal radiation exposure to the fetus 3

Guidelines for CT Use During Pregnancy

• CT should only be performed when the benefits of diagnosis outweigh the potential risks 1
• Abdominal CT without contrast is generally safe, but cumulative ionizing radiation exposure should be kept below 50 mGy 1
• When CT is necessary, proper abdominal shielding should be used to minimize fetal exposure 1
• For suspected pulmonary embolism, CT should be the initial diagnostic imaging modality despite pregnancy 4
• For suspected appendicitis, ultrasound should be the initial modality, with MRI or CT if ultrasound is negative 4

Alternative Imaging Modalities

• Ultrasound without contrast is the preferred initial imaging modality throughout pregnancy 1
• MRI without gadolinium is preferred over CT when ultrasound is inadequate 2, 5
• MRI is safe in all trimesters of pregnancy as no evidence of adverse fetal effects has been demonstrated 2, 5
• Gadolinium-based contrast agents should be avoided during pregnancy due to risks of rheumatologic, inflammatory, or infiltrative skin conditions in offspring and increased risk of stillbirth 1, 2

Contrast Considerations

• Iodinated contrast for CT can potentially cause neonatal hypothyroidism, though most modern CT studies use non-ionic contrast which has no effect on the thyroid gland 1
• Use of iodinated contrast agents should be limited to situations where the diagnostic information would significantly affect the care of the mother or fetus 1
• Less than 0.01% of CT contrast is present in breast milk, making it safe for breastfeeding after contrast administration 1

Clinical Decision-Making

• The risk-benefit analysis should be conducted on a case-by-case basis in consultation with radiologists, obstetricians, and other specialists 1
• In life-threatening situations where rapid diagnosis is essential, CT should not be withheld or delayed due to exaggerated concerns about radiation 6
• For most pregnant patients with new or worsening neurological abnormalities, the risks of the untreated disease will outweigh the risks of imaging 6

Remember that while there are theoretical risks associated with CT during pregnancy, when medically necessary, the benefits of accurate and timely diagnosis typically outweigh these risks. Communication between the referring physician and radiologist is essential to determine the most appropriate imaging strategy.