X-Rays During Pregnancy — Why Avoid It?

Question: Can you explain why pregnant women need to avoid x-rays?

Women are generally advised to avoid chest and dental X-rays during pregnancy. This is to minimize the chances of causing any harm to the fetus. But this applies only to routine or screening X-rays. If an X-ray is needed for medical reasons, it should be done since the benefits far outweigh any risk to the fetus.

Medical science knows more about X-ray exposure to the fetus than about any medication you’d take during pregnancy, including aspirin. X-rays exposure in pregnancy has only ever been shown to cause three effects on the fetus. The list of effects can be scary: miscarriage, a smaller-than-usual brain size, and an increased risk of leukemia in children. Importantly, these effects depend entirely on the time in pregnancy when the exposure was experienced. Also, on the amount (also known as the dose) of X-rays that was used.

How risky is it?

Truth be told, there is no amount of exposure to X rays that can be considered completely safe. However, there does not appear to be any risk to the fetus if the exposure is less than 5 rads. And most effects are only seen when the exposure exceeds 20 rads. Remember that the normal dose of a routine chest or dental X-ray is only 1 to 3 millirads (or 0.001 to 0.003 rads).

This means that a pregnant woman would need to get more than 5,000 chest X-rays in pregnancy before we even got close to the safety threshold. A routine chest or dental X-ray can therefore be regarded as completely safe in pregnancy. In fact, because of the increased background radiation exposure as one gets higher in the stratosphere, an airplane flight from Boston to Los Angeles is associated with a radiation exposure that is equivalent to three chest X-rays in pregnancy.

What if it’s necessary?

Hospital X-ray departments often have posters on the walls advising pregnant women against having unnecessary X-rays. If an X-ray is necessary in pregnancy, every effort should be made to limit the amount of X-rays reaching the fetus. One way is to use a lead apron to shield the abdomen during the exposure, which is done routinely. If you have any questions, ask your health-care provider about any diagnostic imaging or treatment that has been recommended for you. Remember that magnetic resonance imaging does not use radiation. For that reason, MRI is often used in place of X-rays and CT scans in pregnancy.

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Answered by Errol Norwitz, M.D., Ph.D. Dr. Norwitz is internationally recognized for his work in high-risk obstetrics. He is the Chair of Obstetrics & Gynecology at Tufts Medical Center, and a Professor at Tufts University School of Medicine in Boston. He is board certified in Obstetrics & Gynecology and Maternal-Fetal Medicine.