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 exam | Fetal radiation dose (mGy) |
|---|---|
| Extremity x-ray | <0.001 |
| C-spine x-ray | <0.001 |
| Chest x-ray | 0.0005-0.001 |
| Abdominal x-ray | 0.1-3.0 |
| L-spine x-ray | 1.0-10 |
| CT head or neck | 0.001-0.01 |
| CT chest / CT pulmonary angiogram | 0.01-0.66 |
| CT abdomen | 1.3-35 |
| CT pelvis | 10-50 |
| Low dose VQ scan | 0.1-0.5 |
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 exam | Approximate fetal dose in $ | Number of tests needed to get to $50 |
|---|---|---|
| Extremity x-ray | 0.1 cents | 50,000 |
| C-spine x-ray | 0.1 cents | 50,000 |
| Chest x-ray | 0.05 to 1 cent | 5,000 – 100,000 |
| Abdominal x-ray | 10 cents to 3 dollars | 16-500 |
| L-spine x-ray | 1-10 dollars | 5-50 |
| CT head or neck | 0.1 to 1 cent | 5,000-50,000 |
| CT chest / CT pulmonary angiogram | 1 to 66 cents | 75-5,000 |
| CT abdomen | 1 to 25 dollars | 2-50 |
| CT pelvis | 10 to 50 dollars | 1-5 |
| Low dose VQ scan | 10 to 50 cents | 100-5000 |
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
2 thoughts on “Diagnostic imaging during pregnancy and lactation”
Dear Dr. Morgenstern,
This is both interesting and relevant, as usual. Keep up the great work.
I would like to comment on one issue, which you have only mentioned briefly – the radiation exposure to the mother.
This is mostly relevant in the diagnostic work-up of suspected pulmonary emboli in pregnant women, a relatively common condition. In many circumstances, “harmless” tests (D-dimer, duplex sonography, CXR etc.) are not reassuring to exclude PE and we are left with the need for more advanced chest imaging. Both providing anticoagulation without a firm support, or not providing it without appropriate ruling-out are not acceptable, and we need to decide whether to proceed with a CTA or VQ scan, if both are available. As you have just demonstrated, the risk for the fetus by either is negligible. However, the radiation dose to the mothers breasts is much higher for CTA, and in the proliferating tissue associated with pregnancy, this may (at-least theoretically) increase future risk for breast cancer. When you also consider that CTA is less specific in young individuals, especially pregnant women due to increased blood volume and hyperdynamic heart, and that in most cases there is no prior structural lung disease (which should also be assessed by the CXR), then in many cases the perfusion scan alone is good enough to safely rule-out PE without the need for ventilation scan. In such cases there is both better accuracy, and less radiation exposure to both the fetus and the mother (especially breasts/chest wall) with the VA scan.
Thank you for the excellent site,
I agree with your logic, although it overlooks 2 factors that complicate the discussion:
1) CTPA provides a lot more information in a patient with dyspnea / chest pain and may lead to an alternative diagnosis if the PE scan is negative. Furthermore, despite CT angiogram being less accurate in pregnant women, it is still not as inaccurate as a perfusion scan, in which a significant minority of women still need to proceed to CT anyway.
2) I have spoken to hundreds of mothers about this over the last decade, and not a single one cared about their own radiation risk as compared to that of the fetus. The estimates in the post are from ACOG, but in my readings, a perfusion scan likely has higher radiation doses to the fetus, given that the radiative material is concentrated in the bladder prior to being excreted, and mothers seem to universally want to avoid that when given that choice.
I don’t think there is enough certainty to have strong opinions in one way or the other. I still talk through both options with my patients, but at the end of the day almost everyone chooses CT, and I think that is a reasonable choice.