What does PET (Positron Emission Tomography) refer to in pregnancy?

PET in Pregnancy: Pre-Eclampsia Toxemia vs. Positron Emission Tomography

In pregnancy, PET commonly refers to Pre-Eclampsia Toxemia, a hypertensive disorder characterized by high blood pressure and proteinuria developing after 20 weeks gestation, rather than Positron Emission Tomography imaging. 1

Pre-Eclampsia Toxemia (PET)

Pre-Eclampsia Toxemia is a serious pregnancy complication characterized by:

• Hypertension (blood pressure ≥140/90 mmHg) developing after 20 weeks of gestation
• Proteinuria (≥300 mg in 24-hour urine collection)
• Can be associated with elevated lactate dehydrogenase (LDH) levels 1
• May lead to serious maternal and fetal complications if not properly managed

Clinical Significance

• PET is a major cause of maternal and perinatal morbidity and mortality
• Can progress to eclampsia (seizures) or HELLP syndrome (Hemolysis, Elevated Liver enzymes, Low Platelets)
• Requires close monitoring and may necessitate early delivery depending on severity

Positron Emission Tomography (PET) in Pregnancy

While less commonly referred to as "PET" in pregnancy contexts, Positron Emission Tomography is occasionally performed during pregnancy when clinically necessary:

• PET imaging uses radioactive tracers (most commonly 18F-FDG) to detect metabolic activity
• In pregnancy, PET is generally avoided but can be performed with special precautions when benefits outweigh risks 1
• When used in pregnant cancer patients, PET can significantly impact clinical staging and treatment decisions 1

Safety Considerations for PET Imaging in Pregnancy

If PET imaging is deemed necessary during pregnancy:

• Reduced doses of 18F-FDG should be used (2.6E-02 mGy/MBq in first trimester, decreasing to 6.9E-03 mGy/MBq by third trimester) 2

• Fetal radiation exposure can be minimized through:

  • Performing PET alone rather than PET-CT when possible 3
  • Vigorous hydration and urinary catheterization to facilitate rapid elimination of radiopharmaceuticals 1, 4
  • Using lower doses of radiopharmaceuticals with correspondingly longer acquisition times 3

• Estimated fetal radiation doses from modified PET protocols range from 1.1 to 2.43 mGy in second and third trimesters, which is below the threshold for deterministic effects 4

Clinical Applications During Pregnancy

PET imaging during pregnancy is primarily considered for:

• Cancer staging and treatment planning 1
• Assessment of metastatic disease 1
• In a retrospective analysis of 63 cancer patients who underwent PET during pregnancy, PET modified the clinical stage in 60% of patients and affected first-line treatment 1

Diagnostic Alternatives in Pregnancy

When imaging is needed during pregnancy, safer alternatives are typically preferred:

• Ultrasound is the first-line imaging modality for most conditions 1
• MRI without gadolinium can be used when ultrasound is inconclusive 1
• For suspected pulmonary embolism, chest X-ray followed by V/Q scan is preferred over CT-based imaging 3

Conclusion

When encountering "PET" in pregnancy contexts, clinicians should first consider Pre-Eclampsia Toxemia, a serious hypertensive disorder. Positron Emission Tomography imaging, while occasionally necessary in pregnant cancer patients, requires special precautions to minimize fetal radiation exposure and should be performed only when benefits clearly outweigh risks.