Is a chest x-ray (CXR) safe for a 27-week pregnant patient?

Chest X-Ray Safety in Pregnancy at 27 Weeks

Yes, it is safe to perform a chest x-ray on a 27-week pregnant patient—the fetal radiation dose is negligible (<0.01 mGy) and falls far below any threshold for harm. 1

Radiation Exposure Context

The fetal radiation exposure from a standard chest x-ray (posteroanterior and lateral views) is less than 0.01 mGy 1, which represents an extraordinarily small dose. To put this in perspective:

• The established safety threshold for fetal harm is 50-100 mSv (50,000-100,000 mGy) 1
• A chest x-ray delivers approximately 1/5,000,000th of this threshold dose 1
• This exposure is comparable to natural background radiation over a few days 2

Clinical Decision Framework

When to proceed with chest x-ray in pregnancy:

• Proceed without hesitation when clinically indicated for acute symptoms (dyspnea, cough, suspected pneumonia, pulmonary embolism evaluation) 1
• The risk of missing a potentially serious maternal diagnosis far outweighs the negligible radiation risk 1
• Delaying or avoiding necessary imaging poses greater risk to both mother and fetus than the radiation exposure itself 1

The ALARA principle applies: While chest x-rays are safe, they should only be obtained when other non-radiologic methods fail to clarify the diagnosis 1. However, this does not mean avoiding necessary imaging—it means not performing unnecessary studies.

Specific Considerations at 27 Weeks Gestation

At 27 weeks (third trimester), the fetus is past the most radiosensitive period for major malformations:

• The critical window for central nervous system teratogenesis is 10-17 weeks gestation 2
• The most vulnerable period for deterministic effects is 8-15 weeks 3
• At 27 weeks, organogenesis is complete, further reducing theoretical concerns 4

Documented Safety Evidence

Multiple authoritative guidelines confirm chest radiography safety:

• The European Society of Cardiology explicitly states chest radiographs deliver <10 mGy to the fetus, well below safety thresholds 1
• The American College of Cardiology notes that exposures within recommended limits (0.5 rem per pregnancy = 5 mGy) pose no significant risk 1
• No single diagnostic study exceeds the accepted cumulative dose of 5 rad (50 mGy) during pregnancy 2

Theoretical vs. Actual Risk

Stochastic effects (cancer risk): The only statistically proven adverse effect at diagnostic radiation levels is a very small increase in childhood malignancy—estimated at one additional cancer death per 1,700 exposures of 10 mGy 5. Since chest x-ray delivers <0.01 mGy, this risk is essentially unmeasurable 1.

Deterministic effects (malformations, growth retardation): These have threshold doses above 100-200 mGy 3. Chest radiography delivers 1/10,000th of this threshold, making such effects impossible 4.

Common Pitfalls to Avoid

Pitfall #1: Unnecessary anxiety leading to diagnostic delay

• Solution: Counsel the patient that chest x-ray radiation is equivalent to a few days of natural background exposure 2
• Emphasize that missing a serious maternal condition (pneumonia, PE, heart failure) poses far greater risk 1

Pitfall #2: Ordering abdominal shielding

• Modern evidence suggests abdominal shielding for chest x-rays provides no meaningful benefit and may require repeat imaging if positioning is compromised 1
• The scatter radiation to the uterus is already negligible 1

Pitfall #3: Documenting inadequately

• Document the clinical indication clearly in the medical record 1
• Note that risks and benefits were discussed with the patient 1

Patient Counseling Points

When discussing with the patient, emphasize:

• The radiation dose is less than what she receives from natural sources in a few days 2
• No diagnostic x-ray study exceeds safe limits during pregnancy 2, 4
• The examination is necessary to properly diagnose and treat her condition 1
• Missing a serious maternal diagnosis poses greater risk to both her and the baby than the negligible radiation exposure 1