Is a CT scan safe during pregnancy?

What does the evidence say about CT scans during pregnancy?

1. A CT of the pelvis carries the highest fetal radiation dose among common CT exams, at roughly 50 mGy, which sits right at the boundary researchers use to define a dose with a documented negative fetal impact; doses below that are considered safe, and doses in the 50 to 100 mGy range are regarded as inconclusive. 1
2. A fetal radiation dose under 100 mGy is not expected to cause short-term deterministic effects during organogenesis, while a dose of 10 mGy is the level at which researchers begin to consider an increased risk of childhood cancer; for most medically appropriate, correctly performed diagnostic imaging, the added risk to the fetus is minimal. 2
3. A high diagnostic radiation dose after 4 weeks post-conception could raise the risk of childhood cancer to roughly 3 in 500, compared with a background risk of about 1 in 500, which is the framework providers use to weigh whether a scan is worth ordering. 2
4. A CT pulmonary angiogram, a scan used to check for a blood clot in the lungs, exposes the fetus to a relatively low dose (about 0.03 to 0.66 mGy), and diagnostic imaging for a suspected blood clot generally shouldn't be delayed over radiation concerns, since an untreated clot carries its own serious risk; repeated iodine contrast injections are something to use judiciously and preferably avoid when possible in pregnant patients. 3
5. An x-ray dose under 50 mSv hasn't been linked to a higher chance of birth defects, while exposure above about 500 mSv could affect learning, and exposure of more than 100 mSv between roughly the 8th and 15th week of pregnancy has been associated with learning difficulties, thresholds that give useful context for how far a typical diagnostic scan sits from a level of real concern. 4

Is CT scans safe in each trimester?

• First trimester. The fetus is most sensitive to radiation during organogenesis. Effects aren't expected below a fetal dose of about 100 mGy, and most single diagnostic CT scans deliver far less than that, but your care team will still weigh whether a lower-radiation alternative like ultrasound or MRI can answer the same question first.
• Second trimester. The same dose thresholds apply. A medically necessary CT scan generally shouldn't be delayed out of radiation concern once other options have been considered, since an untreated underlying condition can carry its own risk.
• Third trimester. Same guidance continues. If contrast dye is being considered, ask about whether it's needed, since repeated iodine contrast exposure is generally something to use judiciously in pregnancy.