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21 November 2009

Answer to Question #7185 Submitted to "Ask the Experts"

Category: Nuclear Medicine Patient Issues — Diagnostic Nuclear Medicine

The following question was answered by an expert in the appropriate field:

I had a nuclear medicine kidney scan done with technetium-99m MAG-3 (mercapto acetyl triglycine) with a Lasix Washout. I took a urine pregnancy test three days before and the day before the study and all the tests were negative. The nuclear medicine study was performed and then I found out that I was pregnant two days later. How much radiation did the fetus receive and what is the effect on the baby?

I am sorry to hear that you had a radiological study done based on a negative pregnancy test. Unfortunately, that is the status of our medical abilities at this time and there is uncertainty with this test until there is enough of the hormone human chorionic gonadotropin (HCG) to show positive on a blood or urine test. The good news is that the dose to the embryo was very low for this diagnostic exam.

Radiation exposure early in pregnancy causes what we refer to as an "all or none" effect during the first 10 days of pregnancy. If there was enough radiation to do damage, the pregnancy would spontaneously abort. If there was not that much exposure, then the pregnancy should progress normally as the embryo is very resilient at that stage.

If the nuclear medicine study was performed just after that time period, the exposure to the embryo would depend on the amount of technetium-99m MAG-3 you were given. I have seen recommended administrations between 5 millicuries to 10 millicuries. So the dose to the embryo could have been between 0.33 and 0.66 rad. To put that dose into perspective, I will quote from our Web site:

"Most diagnostic procedures expose the embryo to less than 5 rad. This level of radiation exposure will not increase reproductive risks (either birth defects or miscarriage). According to published information, the reported dose of radiation to result in an increase incidence of birth defects or miscarriage is above 20 rad."

So in your case, the highest estimate for dose to the embryo would be 0.66 rad compared to the dose where there would be some concern: 20 rad. Your fetal dose was lower than the lowest level of effect by a factor of 30.

That should reassure you that the exposure that you have experienced is very low and will not increase your risk for birth defects or miscarriage. I hope that this will relieve your concerns, and good luck with your pregnancy.

Marcia Hartman, MS

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