cfDNA vs. Routine Screening – How Do They Compare?
Cell free DNA (cfDNA / NIPS / NIPT) screening tests for fetal Trisomy 21 (Down syndrome) are more sensitive, have lower false positive rates and higher positive predictive values regardless of maternal age, than standard first trimester screening
Despite improved performance compared to standard screening, cfDNA tests should be considered screening tests only. Further counseling and diagnostic confirmation should be sought prior to acting on a positive cfDNA screening test result
Norton and colleagues (NEJM, 2015) reported findings from the NEXT study comparing performance between new prenatal screening tests using cfDNA, compared to first trimester standard screening (serum pregnancy-associated plasma protein A, and total or free beta subunit of human chorionic gonadotropin measurements, with nuchal translucency).
In a general population of women in the first trimester of pregnancy, cfDNA testing detected 38/38 fetuses affected with Trisomy 21 compared to 30/38 with standard screening
The positive predictive value (PPV) was 80.9% using cfDNA compared to 3.4% using standard screening
cfDNA screening did result in some false positives for Trisomy 21
confirmatory/diagnostic testing is therefore required before acting on cfDNA or standard screening tests
cfDNA screening is less ideal for obese patients as suggested in previous studies
“No results” cfDNA reports require additional follow-up to rule out fetal aneuploidy
This study was focused on Trisomy 21 detection only; however results for Trisomy 18 and Trisomy 13 suggest cfDNA provides more accurate screening for these disorders as well
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