Can cell-free DNA (cfDNA) testing be performed in triplet pregnancies?

Cell-Free DNA Testing in Triplet Pregnancies

Cell-free DNA testing is not recommended as a routine screening method for fetal aneuploidy in triplet pregnancies due to limited data on its performance and reliability in this population.

Current Evidence and Recommendations

The 2015 Society for Maternal-Fetal Medicine (SMFM) guideline specifically states that "at this time, the data are too limited to recommend routine cfDNA aneuploidy screening in women with multifetal gestations" 1. This recommendation is based on several important limitations:

• Higher failure rates in multifetal gestations compared to singleton pregnancies
• Potentially lower detection rates for aneuploidies
• Limited number of cases studied, particularly for triplet pregnancies

Recent Research on Triplet Pregnancies

While the SMFM guideline from 2015 remains the most authoritative source, more recent research has begun to explore cfDNA testing in triplet pregnancies:

• A 2024 study examined 255 triplet pregnancies undergoing cfDNA testing, reporting a no-call rate of 2.4% at first sampling 2. This study suggested cfDNA testing could potentially be offered in triplet pregnancies after appropriate patient counseling.

• Another 2024 study included 10 triplet pregnancies, reporting an initial no-result rate of 10.3%, though all eventually yielded results after redraw 3. However, this small sample size limits definitive conclusions.

Practical Considerations and Limitations

When considering cfDNA testing in triplet pregnancies, several important factors should be considered:

1. Technical challenges:

   • Each fetus contributes to the total fetal fraction, making it more difficult to detect abnormalities in any single fetus
   • Higher likelihood of "no-call" results requiring repeat testing

2. Interpretation complexities:

   • If a positive result is obtained, it's impossible to determine which fetus(es) is affected without invasive testing
   • False positive results may occur due to confined placental mosaicism or other biological phenomena

3. Alternative options:

   • Detailed ultrasound examination remains important for all multifetal pregnancies
   • Invasive diagnostic testing (amniocentesis) provides definitive results but carries increased procedure-related risks in multiple gestations

Recommendations for Clinical Practice

For patients with triplet pregnancies seeking aneuploidy screening:

1. Provide thorough counseling about the limitations of cfDNA testing in triplet pregnancies
2. Consider conventional screening methods and detailed ultrasound examination
3. If cfDNA testing is pursued:
   • Emphasize its investigational nature in triplet pregnancies
   • Ensure patients understand the higher likelihood of test failure
   • Clarify that positive results will require invasive testing for confirmation and fetal identification
   • Recognize that negative results do not definitively rule out aneuploidy

Conclusion

While emerging research suggests cfDNA testing may eventually become a viable option for triplet pregnancies, current guidelines do not support its routine use in this population due to limited data on performance and reliability. Patients should be counseled about these limitations and the need for additional testing if abnormalities are suspected.