Return to Search
EN
The cell-free fetal DNA (cfDNA) test is a *screening test*, not a diagnostic one. Its primary purpose is to assess risk, not to definitively diagnose a condition.
Understanding Test Results:
Results are reported as either low risk (typically less than 1 in 10,000 for each chromosome) or high risk (generally over 99%). A positive or high-risk cfDNA result *always requires confirmation* through invasive diagnostic tests.
Follow-up for High-Risk Results:
* Trisomy 21 (Down Syndrome): If the cfDNA result is positive for Trisomy 21 following a first-trimester screening, a Chorionic Villus Sampling (CVS) can be performed for diagnostic confirmation.
* Trisomy 18 (Edwards Syndrome) and Trisomy 13 (Patau Syndrome): In cases of a positive cfDNA result for Trisomy 18 or 13, a detailed ultrasound examination should be conducted. If characteristic anomalies associated with these trisomies are detected, CVS may be considered. However, if no anomalies are found on ultrasound, amniocentesis is the preferred diagnostic test to mitigate the risk of false positives due to confined placental mosaicism.
* Negative/Low-Risk Results: A negative or low-risk cfDNA result provides strong reassurance that the fetus is unlikely to be affected by the trisomies screened for. This can significantly reduce the prior risk (based on maternal age or previous screening methods) by approximately 300-fold for Trisomy 21 and 50-fold for Trisomy 18 and 13.
Key Considerations for Patients:
When discussing non-invasive prenatal aneuploidy screening using cfDNA with patients, it is crucial to cover the following:
* The screening is optional, and alternative screening and diagnostic options are available.
* The specific conditions tested for and, importantly, what the test *does not* detect.
* Associated costs and insurance coverage.
* Turnaround time (typically five to seven days), how results are reported, the possibility of incidental findings, and test performance in twin pregnancies.
Recommended Approach to cfDNA Screening:
Instead of routinely offering cfDNA testing to all pregnant individuals, it is often more effective and cost-efficient to offer it as a secondary screening method to a selected subgroup of the population, specifically those identified as high or intermediate risk following an initial screening, ideally the first-trimester combined test (double test). This approach maintains a very high detection rate and a very low rate of invasive diagnostic procedures, at a significantly lower overall cost compared to universal cfDNA screening.
Universal Recommendations for All Pregnancies:
Regardless of cfDNA screening decisions, all pregnant women should be offered a detailed ultrasound scan between 11-13 weeks for early detection of major fetal anomalies and early preeclampsia screening to identify individuals who may benefit from aspirin prophylaxis.
About the Fetal DNA Test
Understanding Test Results:
Results are reported as either low risk (typically less than 1 in 10,000 for each chromosome) or high risk (generally over 99%). A positive or high-risk cfDNA result *always requires confirmation* through invasive diagnostic tests.
Follow-up for High-Risk Results:
* Trisomy 21 (Down Syndrome): If the cfDNA result is positive for Trisomy 21 following a first-trimester screening, a Chorionic Villus Sampling (CVS) can be performed for diagnostic confirmation.
* Trisomy 18 (Edwards Syndrome) and Trisomy 13 (Patau Syndrome): In cases of a positive cfDNA result for Trisomy 18 or 13, a detailed ultrasound examination should be conducted. If characteristic anomalies associated with these trisomies are detected, CVS may be considered. However, if no anomalies are found on ultrasound, amniocentesis is the preferred diagnostic test to mitigate the risk of false positives due to confined placental mosaicism.
* Negative/Low-Risk Results: A negative or low-risk cfDNA result provides strong reassurance that the fetus is unlikely to be affected by the trisomies screened for. This can significantly reduce the prior risk (based on maternal age or previous screening methods) by approximately 300-fold for Trisomy 21 and 50-fold for Trisomy 18 and 13.
Key Considerations for Patients:
When discussing non-invasive prenatal aneuploidy screening using cfDNA with patients, it is crucial to cover the following:
* The screening is optional, and alternative screening and diagnostic options are available.
* The specific conditions tested for and, importantly, what the test *does not* detect.
* Associated costs and insurance coverage.
* Turnaround time (typically five to seven days), how results are reported, the possibility of incidental findings, and test performance in twin pregnancies.
Recommended Approach to cfDNA Screening:
Instead of routinely offering cfDNA testing to all pregnant individuals, it is often more effective and cost-efficient to offer it as a secondary screening method to a selected subgroup of the population, specifically those identified as high or intermediate risk following an initial screening, ideally the first-trimester combined test (double test). This approach maintains a very high detection rate and a very low rate of invasive diagnostic procedures, at a significantly lower overall cost compared to universal cfDNA screening.
Universal Recommendations for All Pregnancies:
Regardless of cfDNA screening decisions, all pregnant women should be offered a detailed ultrasound scan between 11-13 weeks for early detection of major fetal anomalies and early preeclampsia screening to identify individuals who may benefit from aspirin prophylaxis.