Answer to Question #11549 Submitted to "Ask the Experts"

Category: Pregnancy and Radiation — Radiation effects to embryo/fetus

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


I perform computed tomography (CT) scans in a hospital. A few days ago, I performed a CT scan on a woman's pelvis. The protocol used for this examination results in a dose to the patient between 10 and 15 milligray (mGy).

At the time of the CT scan, I did not know the patient was four weeks pregnant. Now I feel great guilt. Please tell me frankly if there will be an effect on the fetus.


With a dose that small and at just four weeks into the pregnancy, the risk for harmful effects is low.

We believe the most sensitive period of a pregnancy for possible harmful effects to the fetus from radiation is at 8–15 weeks with radiation doses above 50 mGy. Below this radiation dose, while there may be some increased risk, the natural background risk of birth defects (3% of births) and miscarriage (15% of births) far exceed any risk from the radiation exposure.

The Health Physics Society's fact sheet on "Radiation Exposure and Pregnancy" might be a good resource for you.

From what we know about the risk of radiation exposure to a developing fetus, it is unlikely the radiation dose from the CT scan caused any harmful effects.

Kelly Classic
Certified Medical Health Physicist

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
Answer posted on 4 April 2016. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.