Safety of Radiological Examinations During Pregnancy: Importance and Recommendations

The use of X-rays, ultrasound waves, computed tomography (CT), nuclear medicine techniques, and magnetic resonance imaging (MRI) has become an indispensable part of modern medicine. Consequently, during pregnancy, many women will either incidentally or based on clear indications undergo some of these diagnostic techniques. Concerns about the safety of radiological examinations in pregnant or breastfeeding women, as well as the safety of the fetus, often lead to unnecessary avoidance of useful diagnostic procedures.

During pregnancy, radiation exposure applies not only to the mother but also, potentially, to the fetus. It should be emphasized from the outset that in most situations where a pregnant woman may be exposed to radiation—such as diagnostic medical imaging or occupational exposure—the radiation doses fall within prescribed limits and are unlikely to cause adverse health effects in the fetus.

The human embryo and fetus are sensitive to ionizing radiation at doses exceeding 0.1 Gy (100 mGy). Depending on the stage of fetal development, health consequences may occur at doses above 0.5 Gy (500 mGy), which can be severe. A fetal radiation dose below 50 mGy carries negligible risk for miscarriage or malformations compared to other pregnancy risks. A fetal dose below 100 mGy should not be considered a reason for medical termination of pregnancy.

Table 1. Fetal Radiation Exposure in Common Radiological Procedures

Very Low Dose Examinations (<0.1 mGy):

• Cervical spine X-ray (AP and lateral): <0.001

• Head and neck CT: 0.001–0.01

• Extremity X-ray: <0.001

• Mammography: 0.001–0.01

• Chest X-ray: 0.0005–0.01

Low to Moderate Dose Examinations (0.1–10 mGy):

• Abdominal X-ray: 0.1–3.0

• Lumbar spine X-ray: 1.0–10

• Intravenous pyelography: 5–10

• Chest CT or pulmonary CT angiography: 0.01–0.66

• Nuclear medicine low-dose perfusion scan: 0.1–0.5

• Bone scintigraphy with technetium: 4–5

• Pulmonary digital subtraction angiography: 0.5

High Dose Examinations (10–50 mGy):

• Abdominal CT: 1.3–35

• Pelvic CT: 10–50

• Whole-body PET-CT: 10–50

Radiation Exposure in Specific Imaging Procedures

• Ultrasound (US): Uses sound waves and does not involve ionizing radiation. When performed correctly with properly calibrated equipment, it poses no risk to the fetus or pregnancy.

• Magnetic Resonance Imaging (MRI): Uses magnetic fields rather than ionizing radiation. There are no pregnancy-specific contraindications.

• MRI Contrast Agents: Gadolinium-based contrast agents should be used only when the diagnostic benefit clearly outweighs potential risks.

• X-rays: Often indicated during pregnancy or performed inadvertently before pregnancy is detected. Examinations not directly involving the abdomen or fetus result in radiation doses far below the natural background radiation exposure during pregnancy. Dental, chest, and extremity X-rays are therefore considered safe. Even multiple diagnostic X-rays rarely expose the fetus to significant radiation.

• Computed Tomography (CT): With or without contrast, CT may be performed during pregnancy if there is a clear clinical indication and the benefits outweigh the risks.

• Nuclear Medicine: Pregnancy is not always a contraindication for nuclear medicine procedures, particularly those using radionuclides with short half-lives, provided there is a strong clinical indication and radiation-free alternatives are unsuitable. In life-threatening maternal conditions, radionuclides may be used, with prior evaluation of the absorbed fetal dose and risks.

Professional Recommendations for Radiological Imaging in Pregnancy

The Committee on Obstetric Practice of the American College of Obstetricians and Gynecologists (2019) summarized the following guidance:

• Ultrasound and MRI are not associated with radiation risks and are the first-line imaging choices during pregnancy. They should, however, be used judiciously, only when they are expected to answer relevant clinical questions or provide medical benefit.

• With few exceptions, radiation doses from conventional X-rays, CT, or nuclear medicine are well below thresholds associated with fetal harm. If clinically indicated, these examinations should not be withheld from pregnant women.

• Gadolinium-based contrast agents in MRI should be restricted to cases where they significantly improve diagnostic accuracy or outcomes for mother or fetus.

Conclusion

Radiological imaging techniques are widely used in medicine and may also be indicated during pregnancy. Although some involve ionizing radiation, fetal exposure is typically below levels that could cause congenital malformations, miscarriage, or termination. For most pregnant women, ultrasound and MRI remain first-line diagnostic tools, but when clinically necessary, ionizing radiation-based procedures should not be denied.

References:

1. ACOG. Guidelines for Diagnostic Imaging During Pregnancy and Lactation. Dostupno na: https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/10/guidelines-for-diagnostic-imaging-during-pregnancy-and-lactation Pristupljeno 25.4.2024.

2. Lowe S. Diagnostic imaging in pregnancy: Making informed decisions. Obstet Med. 2019 Sep;12(3):116-122. doi: 10.1177/1753495X19838658. Epub 2019 Apr 11. PMID: 31523267; PMCID: PMC6734637.

3. Kruskal JB. Diagnostic imaging in pregnant and lactating patients. UpToDate. Pristupljeno 29.4.2024.