What should the provider do if a patient is found to be pregnant in her first trimester after an X-ray has been ordered?

What to Do When Pregnancy is Discovered After X-ray Order in First Trimester

The provider should confirm fetal gestational age first, then proceed with standard imaging protocol using appropriate radiation safety measures, as diagnostic X-rays outside the abdomen/pelvis pose negligible fetal risk (<1 mGy) and should not be deferred when clinically indicated. 1

Immediate Action: Confirm Gestational Age

• Determine precise gestational age using first-trimester ultrasound crown-rump length (CRL) measurement, which is accurate within ±5-7 days and is the gold standard for pregnancy dating. 2
• Document both last menstrual period (LMP) and ultrasound-based dates, but use the ultrasound-based date for all clinical decisions. 2
• Accurate dating is critical because fetal radiation sensitivity varies by gestational stage, with the most vulnerable period being 8-15 weeks for deterministic effects. 3

Proceed with Imaging Using Standard Protocol

• For extremity and cervical spine radiographs, proceed with standard imaging protocol as these expose the fetus to minimal radiation (<10 mGy), well below the 50 mGy safety threshold. 1, 3
• Women can be reassured that benefit far outweighs risk for diagnostic imaging when radiographs and CT scans do not involve the abdomen or pelvis, as predicted fetal absorbed dose is less than 1 mGy. 1
• The threshold for significant fetal damage is 100 mGy, with no detectable increases in adverse outcomes (malformations, growth restriction, fetal death) below 50 mGy. 4

Risk Stratification by Anatomic Location

High-risk imaging (requires modification):

• Pelvis radiograph: approximately 1.1 mGy fetal dose 1
• Pelvis CT: approximately 25-35 mGy fetal dose 1, 3
• For suspected appendicitis in first trimester: perform pregnancy testing prior to imaging, then use ultrasound or MRI instead of CT. 1

Low-risk imaging (proceed with standard protocol):

• Chest X-ray: <0.01 mGy fetal dose 4
• Extremity radiographs: <10 mGy fetal dose 3
• Cervical spine radiographs: <10 mGy fetal dose 3

Documentation and Consent Requirements

• Document the clinical indication and risk-benefit assessment in the medical record when imaging is clinically indicated in pregnancy. 4
• Discuss benefits and risks with the patient, but do not defer clinically necessary imaging based solely on pregnancy status. 5, 6
• The primary consideration should be maternal benefit of accurate diagnosis, not fetal radiation exposure, when the latter is negligible. 4

Common Pitfalls to Avoid

• Do not defer indefinitely or cancel clinically indicated imaging outside the abdomen/pelvis based solely on first trimester pregnancy. 1, 4
• Do not prioritize image quality over dose reduction—use low-dose protocols when CT is required. 4
• Avoid unnecessary imaging studies, but do not withhold necessary diagnostic tests due to unfounded radiation fears. 6, 7
• For pregnant patients with suspected pulmonary embolism, perform chest X-ray first (rating 9/9), then proceed to CTA chest if needed (rating 7/9), as fetal dose remains <0.3 mGy. 1

Alternative Modalities When Appropriate

• Ultrasound without contrast is first-line for abdominal/pelvic imaging throughout pregnancy. 4
• MRI without gadolinium is second-line when ultrasound is inadequate, as it provides detailed images without ionizing radiation. 4
• Avoid gadolinium-based MRI contrast, as it crosses the placenta and has been associated with increased risk of stillbirth, neonatal death, and rheumatologic conditions in offspring. 4