Answer to Question #11481 Submitted to "Ask the Experts"

I am trying to find information regarding how much flying is considered safe during pregnancy with regard to radiation exposure. The overall consensus online seems to be that the dose should be no more than 1 millisievert (mSv) during a 40-week pregnancy. I have read that the "occasional" traveler will be fine and will not risk approaching this limit, but the "frequent" traveler should use caution. There is no information on what constitutes an "occasional" traveler or a "frequent" traveler.

I live in California and would like to plan another cross-country trip home to Virginia to visit family before my baby is born. I am also considering attending educational conferences for work. I am wondering how much more I can travel before I start approaching the 1 mSv limit and go from being an "occasional" traveler to a "frequent" traveler.

During the week of conception, I flew one cross-country flight from Delaware home to California. At four weeks pregnant, I flew a round-trip from California to Delaware. At 15 weeks pregnant, I flew cross-country from California to Virginia, then internationally from Virginia to Ireland. At 16 weeks pregnant, I flew internationally from Ireland home to California.

I would like to fly cross-country to Virginia to visit family when I am 29 weeks pregnant. I would also like to fly to southern California to attend an educational conference. I am hoping you can help differentiate an "occasional" traveler from a "frequent" traveler, as well as objectively define how much travel (hours, distance, or examples of flights) is needed before one approaches 1 mSv. I have a medical background, but no background in radiation science, so I really appreciate any information you can provide.

Let's look at some general information so you can make a more informed decision. For our purposes here, we will use a radiation dose of 0.01 mSv per hour of flight time for a commercial flight. The radiation dose can vary slightly depending on the altitude—international flights are generally at a higher altitude (a bit more radiation) and flights across the United States are generally at a lower altitude (a bit less radiation). So a flight across the country would be about 0.04 mSv and a flight to Ireland might be about 0.07 mSv, as examples. You know better than I what your actual flight times were.

I'm not sure where the 1 mSv suggested limit comes from, but it is not a regulatory limit for a pregnant individual who is flying. I suspect it's been talked about because it is the dose limit to a member of the population who might live around or be inside of organizations using x rays and radioactive materials. For comparison, the regulatory dose limit to a pregnant worker who is exposed occupationally (like an x-ray technologist) is 5 mSv. But neither of these numbers has much to do with potential biological effects as the dose needed to cause harmful effects to a fetus are above 100 mSv (Hall and Giaccia 2006, Wagner et al. 1997). It would take a lot of flying time to get close to 100 mSv.

Now you have some factual information on which you can make your decision whether to fly some additional trips. So far, it looks like you've received about 0.25–0.30 mSv from your flights. This is well below radiation doses that cause harmful fetal effects.

If it were me, I wouldn't be concerned about the radiation dose while flying. Do keep in mind, though, that even if you are healthy and young and have no reproductive problems or family history of reproductive problems, your risk for birth defects is 3% and for miscarriage is 15%. Those are the background rates for effects in the United States.

Kelly Classic
Certified Medical Health Physicist

References
Hall EJ, Giaccia AJ. Radiobiology for the radiologist. 6th ed. New York: Lippincott Williams & Wilkins; 2006.

Wagner LK, Lester RG, Saldana LR. Exposure of the pregnant patient to diagnostic radiations. 2nd ed. Madison, Wisconsin: Medical Physics Publishing; 1997.