Answer to Question #1503 Submitted to "Ask the Experts"

Q

I am 35 weeks pregnant and am being asked to get a chest x ray. How safe is it for the baby? (In one earlier response to a similar question it said "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, 15%. Neither you nor I can change that risk.") In another response your site says there is risk only in the first two trimesters. Please clarify.

A

Someone else provided that information about the period of the pregnancy that the embryo is vulnerable to the effects of irradiation. In the third trimester you need higher doses of radiation to affect the embryo deleteriously. I understand your concern and I will try to explain why your anxiety and concern is not warranted in your present situation. When you receive a diagnostic x-ray study of your head, teeth, chest, arms, or legs at a qualified facility, the exposure of the x rays is not to your embryo. The "scatter" that might reach the embryo would be extremely small and would not represent an increased risk for birth defects or miscarriage to your embryo. The most important characteristic of x rays that concerns us is the dose. You may not know that we ourselves are radioactive and we are exposed to many sources of natural radiation that we cannot avoid. Your developing embryo did not receive a dose that would result in any measurable increased reproductive risk. 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, 15%. Neither you nor I can change that risk which all mothers have when they begin a pregnancy. Good luck with your pregnancy. Robert L. Brent, MD, PhD