The dose of radiation that is generally considered the threshold of safety during pregnancy in 50 milli-Grays.
For context, remember that a transcontinental airplane flight has an approximate radiation dose of 0.01 mGy and the total radiation dose in the average pregnancy is 1 mGy.
| Body Part | X-Ray (mGy) | CT scan (mGy) |
| Face | 0.01 | |
| Chest | 0.01 | 0.06 |
| Mammography | 0.05 | |
| Pelvis | 1.1 | 25 |
| Abdomen | 1.4 | 8.0 |
| Lumbar Spine | 1.7 | 2.4 |
| Head | 0.005 |
Cancer risks are very hard to estimate, but a 10-20 mGy radiation exposure might increase leukemia by a factor of 1.5-2. Given the baseline risk of 1 in 3000, this means that the absolute risk increase of a direct pelvic CT is about 1 in 3000. Phrased differently, you have a 99.97% chance of being perfectly fine even with a high risk exposure (such as a pelvic CT).
Full post: Diagnostic imaging during pregnancy and lactation
Handouts:
Unity Health: Can I have an X-ray or CT scan while I am pregnant?
References
Committee Opinion No. 723: Guidelines for Diagnostic Imaging During Pregnancy and Lactation. Obstet Gynecol. 2017 Oct;130(4):e210-e216. doi: 10.1097/AOG.0000000000002355. Erratum in: Obstet Gynecol. 2018 Sep;132(3):786. PMID: 28937575