Diagnostic imaging during pregnancy and lactation

Diagnostic imaging during pregnancy and lactation
Cite this article as:
Morgenstern, J. Diagnostic imaging during pregnancy and lactation, First10EM, November 20, 2023. Available at:
https://doi.org/10.51684/FIRS.132793

When caring for pregnant women, I frequently find myself searching for information on radiation risks from diagnostic imaging, to help guide our shared decision making process, so I decided to create a summary in a spot I would always know where to find it.

I have ranted in the past about the many problems with medical guidelines. Almost universally, when I do deep dives into the science behind guidelines, I find contradictions or mistakes. I want to be very clear, unlike most other posts on this site, I have not delved deeply into the underlying research here. I am just summarizing the most up to date guidelines I could find. 

The paper: 

Committee Opinion No. 723: Guidelines for Diagnostic Imaging During Pregnancy and Lactation. Obstet Gynecol. 2017 Oct;130(4):e210-e216. doi: 10.1097/AOG.0000000000002355. PMID: 28937575

Key recommendation (in my mind)

“With few exceptions, radiation exposure through radiography, CT scan, or nuclear medicine imaging techniques is at a dose much lower than the exposure associated with fetal harm. If these techniques are necessary in addition to ultrasonography or MRI or are more readily available for the diagnosis in question, they should not be withheld from a pregnant patient.”

Obviously, MRI and ultrasound don’t have any radiation and are preferred if they are available and can answer the clinical question.

Radiation and pregnancy

Although there are some principles to follow, such as “ALARA” or “as low [radiation] as reasonably achievable”, nothing in life is black and white. In order to protect the health of the fetus, we must also protect the health of the mother, and that often means using x-ray or CT to make an important diagnosis. The risk from radiation is actually much smaller than people think, and must be balanced against the risk of a missed diagnosis. Ultimately, there is no definitive right answer in most situations, so we must involve our patients in shared decision making. In order to do that, we need to understand the radiation exposure of the tests we order, and how that compares to the baseline risk in pregnancy.

It is estimated that a fetus will be exposed to 1 mGy of background radiation during an average pregnancy. A transcontinental flight is estimated to have a 0.01 mGy exposure. 

There have not been any reported fetal harms with radiation exposures less than 50 mGy. This is a very conservative estimate.  

Cancer risks are very hard to estimate, but a 10-20 mGy radiation exposure might increase leukemia by a factor of 1.5-2. Given the baseline risk of 1 in 3000, this means that the absolute risk increase of a direct pelvic CT is about 1 in 3000. Phrased differently, you have a 99.97% chance of being perfectly fine even with a high risk exposure (such as a pelvic CT).

This document focuses on fetal risk, but the mother usually receives more radiation and has a higher radiation risk from medical imaging. 

What is the actual radiation exposure of this test?

For context, remember that a transcontinental airplane flight has an approximate radiation dose of 0.01 mGy and the total radiation dose in the average pregnancy is 1 mGy.

Type of examFetal radiation dose (mGy)
Extremity x-ray<0.001
C-spine x-ray<0.001
Chest x-ray0.0005-0.001
Abdominal x-ray0.1-3.0
L-spine x-ray1.0-10
CT head or neck0.001-0.01
CT chest / CT pulmonary angiogram0.01-0.66
CT abdomen1.3-35
CT pelvis10-50
Low dose VQ scan0.1-0.5
** These are the estimates from the ACOG guideline. Numbers vary from source to source, and ACOG seems to use a higher estimate than many sources. Numbers might vary by a factor of 2-3x (with ACOG using the higher end of the spectrum), but the estimates are well within an order of magnitude. 

How do I translate these numbers for my patient?

Personally, I find these numbers confusing. I can’t even imagine trying to sort through them while feeling sick and stressed out as a patient in the emergency department. Because most people are used to thinking and budgeting with money, a brilliant colleague, Dr. Hanna Bielawska, translates these numbers into dollars, with an overall “budget” of $50 representing 50 mGy (or the threshold below which there does not seem to be any fetal risk). 

Type of examApproximate fetal dose in $Number of tests needed to get to $50
Extremity x-ray0.1 cents50,000
C-spine x-ray0.1 cents50,000
Chest x-ray0.05 to 1 cent5,000 – 100,000
Abdominal x-ray10 cents to 3 dollars16-500
L-spine x-ray1-10 dollars5-50
CT head or neck0.1 to 1 cent 5,000-50,000
CT chest / CT pulmonary angiogram1 to 66 cents75-5,000
CT abdomen1 to 25 dollars2-50
CT pelvis10 to 50 dollars1-5
Low dose VQ scan10 to 50 cents100-5000

CT contrast

Oral contrast is not a concern.

IV contrast will cross the placenta, but there is no known harms. Animal studies have not shown mutagenesis or teratogenesis, and despite the iodine, human studies have not shown any thyroid disease. However, there is still lots unknown, so like all interventions, only use contrast if actually necessary. 

Less than 1% of contrast will make it into breast milk, and less than 1% will be absorbed from the child’s GI tract, so contrast is fine while breastfeeding. 

A few points about MRI

Gadolinium is thought to be teratogenic. Gadolinium should be limited and only used if it will significantly improve diagnostic performance and the diagnosis is expected to significantly improve fetal or maternal outcomes. (This choice has never come up for me.)

Breastfeeding should not be interrupted after gadolinium. 

References

Committee Opinion No. 723: Guidelines for Diagnostic Imaging During Pregnancy and Lactation. Obstet Gynecol. 2017 Oct;130(4):e210-e216. doi: 10.1097/AOG.0000000000002355. Erratum in: Obstet Gynecol. 2018 Sep;132(3):786. PMID: 28937575


More rapid reviews can be found here.

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