Answer to Question #2438 Submitted to "Ask the Experts"

Q

How much radiation is dangerous for the unborn fetus in the first trimester? Our office has recently discovered that the radiation oncology equipment on the floor below us has "leaked" through a crack in our floor. The leak was supposedly fixed, however, when I ask to see the reports of their tests before and after, suddenly there is a big investigation and so far they will not devulge any information. There have been four late 1st trimester miscarriages in our office in the past two years with no successful pregnancies. An ultrasound of my unborn, dead fetus prior showed Down Syndrome. Is this a deformation that excessive radiation could have caused?

A

I am sorry that you have concerns about radiation exposure at your place of employment. Not knowing the exposure is certainly disconcerting. I can give you some good news, at least in one respect. Since the radiation equipment is on the floor below you, most of the radiation that is performed is directed down or sideways. You did not tell me your location. But if you are in the United States, radiation facilities are built to certain standards, which includes lead shielding.

Now I will answer your questions. Radiation during pregnancy cannot cause Down Syndrome. It is due to an abnormal development of the egg before fertilization that results in an extra chromosome in the egg that was fertilized. It is not a radiation-induced phenomenon. The dose of radiation to produce a miscarriage late in the first trimester would have to be quite high, probably greater than 50 rad (0.5 Gy). Furthermore it would have to be an acute dose (over a short period of time). This would be very unlikely to be possible from a leak. The lower the dose-rate the lower the risk. In fact, studies have shown that an embryo can receive 2 rad per day, protracted radiation and not have an increased risk of miscarriage. Tell your employers that it would be in the best interest for everyone to reveal the exposure level. It is most likely too low to account for any reproductive effects. Remember that 15% of pregnant women miscarry.

Robert L. Brent, MD, PhD, DSc