What are the risks and recommendations for using radiation-based imaging in a pregnant female?

Radiation-Based Imaging in Pregnancy: Risks and Recommendations

Diagnostic radiation imaging should be performed without hesitation when clinically indicated during pregnancy, as the fetal radiation doses from standard diagnostic studies are far below the threshold for any adverse effects, and the risk of missing a serious maternal diagnosis far outweighs the negligible radiation exposure. 1

Radiation Safety Thresholds

The established safety thresholds provide clear guidance for clinical decision-making:

• Fetal doses below 50 mGy carry no detectable risk of malformations, growth restriction, or fetal death 1
• The threshold for significant fetal damage is 100 mGy 2, 1
• Most diagnostic X-ray studies deliver far less than 20 mGy to the uterus, including single-phase abdominal CT 1
• The accepted cumulative dose during pregnancy is 50 mGy (5 rad), and no single diagnostic study exceeds this maximum 1, 3

The only statistically proven adverse effect at diagnostic radiation levels is a very small increase in childhood malignancy—approximately one additional cancer death per 1,700 exposures at 10 mGy 4. While this represents a doubling of relative risk, the absolute risk remains extremely low given that baseline childhood cancer mortality is only 1-2.5 per 1,000 2.

Imaging Modality Selection Algorithm

First-line: Ultrasound for all anatomic regions where applicable 2, 1, 5

Second-line: MRI without gadolinium when ultrasound is inadequate or inconclusive 2, 1, 5

Third-line: Radiation-based imaging (X-ray or CT) when diagnosis cannot be made with ultrasound/MRI or when rapid diagnosis is essential 1

Radiation Exposure by Anatomic Region

Minimal Risk Studies (Perform Without Hesitation)

• Chest X-ray: <0.01 mGy fetal dose—approximately 1/5,000,000th of the safety threshold 1
• Head/neck CT: <0.01 mGy fetal dose 1, 6
• Extremity radiographs: <1-10 mGy with proper shielding 1
• Chest CT: 0.3 mGy fetal dose 1

Low Risk Studies (Safe When Clinically Indicated)

• Pelvis radiograph: 1.1 mGy fetal dose 1
• Single-phase abdominal CT: <20 mGy 1

Higher Dose Studies (Use Only When Benefit Clearly Outweighs Risk)

• CT abdomen/pelvis: 25-35 mGy fetal dose—should be avoided when possible but may be performed in life-threatening situations 2, 1

Contrast Agent Considerations

Iodinated Contrast (Preferred if Contrast Required)

• Iodinated IV contrast appears safer than gadolinium-based agents 1, 6
• Modern non-ionic iodinated contrast carries minimal theoretical risk of neonatal hypothyroidism 1, 6
• Less than 0.01% appears in breast milk, making breastfeeding safe after administration 1
• Use only when absolutely required to obtain diagnostic information that would affect clinical management 1, 7

Gadolinium-Based Contrast (Avoid)

• Gadolinium should be avoided during pregnancy unless absolutely necessary 2, 1, 5
• Gadolinium crosses the placenta and accumulates in amniotic fluid and fetal tissues 5
• Associated with increased risk of stillbirth, neonatal death, and rheumatologic/inflammatory skin conditions in offspring 1, 5
• MRI without gadolinium is preferred throughout all trimesters 2, 1, 5

Clinical Decision-Making Framework

Document the following in the medical record:

1. Clinical indication for imaging 1
2. Risk-benefit assessment demonstrating medical necessity outweighs potential fetal risks 2, 1
3. Consideration of alternative non-radiation modalities 1
4. Pregnancy status confirmation for women of childbearing age 1

Key principle: Delaying or avoiding necessary imaging poses greater risk to both mother and fetus than the radiation exposure itself 1. The medical necessity must drive the decision, not theoretical radiation concerns 6.

Radiation Protection Principles

• Follow ALARA (As Low As Reasonably Achievable) to minimize exposure 1
• Use proper abdominal shielding when feasible, though modern evidence shows limited benefit for chest X-rays 1
• Collimate the field to the area of interest 1
• Use low-dose CT protocols when CT is required 1
• Keep cumulative ionizing radiation exposure below 50 mGy 1

Timing Considerations

The most sensitive period for central nervous system teratogenesis is 10-17 weeks of gestation 3. However, even during this window, diagnostic radiation doses remain far below harmful thresholds. The first trimester represents the period of organogenesis where theoretical concerns are highest, though actual risk at diagnostic doses remains negligible 8, 4.

Common Pitfalls to Avoid

Do not create unnecessary anxiety leading to diagnostic delay—counsel patients that most diagnostic X-rays deliver radiation equivalent to a few days of natural background exposure 1

Do not defer chest X-rays due to pregnancy concerns—the fetal dose is 10,000 times lower than the threshold for harm 6

Do not use abdominal shielding for chest X-rays—it provides no meaningful benefit and may require repeat imaging if positioning is compromised 1

Do not use radioactive iodine after 12 weeks gestation—it crosses the placenta and affects the fetal thyroid 1, 4

Special Clinical Scenarios

Suspected pulmonary embolism: Perform chest X-ray first, then proceed to CTA chest if needed—the fetal dose remains <0.3 mGy 1

Suspected appendicitis in first trimester: Perform pregnancy testing, then use ultrasound or MRI instead of CT 1

Polytrauma evaluation: TAP CT should not be avoided due to pregnancy if it is the most appropriate and rapidly accessible diagnostic tool 2