Does a Ventilation-Perfusion (VQ) scan expose the fetus to radiation if the mother is pregnant?

Radiation Exposure from V/Q Scan During Pregnancy

Yes, V/Q scans do expose the fetus to radiation, but the fetal radiation dose is very low (approximately 0.1-0.3 mGy) and well below the threshold associated with fetal complications. 1

Radiation Exposure to Fetus from V/Q Scan

• The fetal radiation dose from a V/Q scan is typically less than 1 mGy 2
• This exposure is significantly below the 5 rad (50 mGy) threshold considered safe during pregnancy 3
• For context:
  • The natural background radiation during pregnancy is approximately 0.5-1 mGy
  • The threshold for potential fetal harm is 50-100 mGy 1
  • Fetal malformation risk only increases above background levels at radiation doses >15 rads (150 mGy) 4

V/Q Scan vs. CT Pulmonary Angiography (CTPA)

When imaging is necessary for suspected pulmonary embolism in pregnancy:

• V/Q scan is the preferred first-line imaging for pregnant women with normal chest X-ray 4
• V/Q scan delivers less radiation to maternal breast tissue (0.98-1.07 mGy) compared to CTPA (10-60 mGy) 4
• While CTPA may deliver slightly less fetal radiation in the first trimester, this difference is minimal compared to the significant difference in maternal breast radiation exposure 2

Risk Reduction Strategies

To minimize radiation exposure during V/Q scanning:

• Use half the usual administered activity of Technetium-99m for perfusion scan and increase scan time 4
• When possible, use Xenon-133 for ventilation scan instead of Tc-99m aerosol (lower maternal effective dose) 4
• Consider hydration and encourage frequent urination to reduce fetal exposure 4
• Some experts recommend omitting the ventilation scan, though this may decrease diagnostic accuracy 4

Clinical Perspective

• The risk of missing a potentially fatal pulmonary embolism far outweighs the minimal radiation risk to the fetus 1
• A study linking administrative and healthcare databases found no significant increase in cancer risk in children of mothers who underwent radionuclide imaging during pregnancy 4
• The absolute increase in childhood cancer risk from fetal radiation exposure under 5 rads is estimated to be from 0.1% to 0.2% 4

Important Considerations

• Chest X-ray is recommended as the first radiation-associated procedure before proceeding to V/Q scan 4
• For pregnant women with abnormal chest X-ray, CTPA may be preferred over V/Q scan 4
• The benefits and risks of diagnostic imaging should be discussed with the pregnant woman, emphasizing that the risk of missing a potentially fatal diagnosis outweighs radiation concerns 1

In summary, while V/Q scans do expose the fetus to a small amount of radiation, this exposure is minimal and considered safe. The diagnostic benefits in detecting a potentially life-threatening pulmonary embolism clearly outweigh the theoretical risks of this low-level radiation exposure.