Top 5 things to know about QNatal® Advanced prenatal cfDNA screening

QNatal® Advanced is a noninvasive cell-free DNA (cfDNA) screen. It is a very sensitive and specific screening test for common fetal aneuploidies, including Trisomy 21 (Down syndrome), Trisomy 18, Trisomy 13, as well as certain sex chromosome abnormalities and microdeletions. Although used frequently, there are still many misconceptions about the test. We discuss some key facts below to help patients and providers understand this type of testing.

Prior to testing, patients should be informed about the conditions that can be identified. Since QNatal® is a screening test, any abnormal results indicate an increased chance for a condition and should be followed up by diagnostic testing.

QNatal® does not diagnose or rule out chromosome abnormalities. Like maternal serum screens (MSS), QNatal® has the potential for both false-positive and false-negative results; however, the sensitivity and specificity of QNatal® far exceeds any MSS. Reasons for false positive and false negative results for QNatal® include placental mosaicism (when the chromosomes in the placenta are different than the chromosomes in the fetus), a vanishing twin or co-twin demise, or an underlying maternal chromosome condition. Therefore, when the screen is positive, the patient may consider a chorionic villus sampling (CVS) or amniocentesis after genetic counseling, or choose to have diagnostic testing after birth. Likewise, when the screen is negative, the patient should be advised that the risk for the tested conditions is reduced, but not eliminated. Some patients may elect to have a CVS or amniocentesis without screening, because they may want the additional reassurance of a diagnostic test.

There is an incredible team of scientists behind QNatal®. Quest Diagnostics has over 40 years of genetic testing experience and offers more than 700 genetic tests. QNatal® tests are reviewed by American Board of Medical Genetics and Genomics (ABMGG) board certified MDs and PhDs.  In addition, a dedicated team of QNatal® Genomic Science Specialists, all certified by the American Board of Genetic Counselors (ABGC), are available to clinicians and patients from 8:30AM to 8:00PM ET Monday through Friday.  All abnormal QNatal® results are proactively called directly to the provider.

Fetal fraction is important! The cfDNA analyzed by QNatal® is composed of fragments from both maternal cells and the placenta. The relative amount of placental cfDNA is referred to as the fetal fraction (FF) and will increase throughout pregnancy as the placenta (and the fetus) grows. The FF must amount to at least 3.5%-4.5% of the cfDNA present in order for QNatal® to assess for fetal aneuploidy. The test cannot be performed for samples not meeting this threshold. At a later gestational age, a new sample will be requested from the patient.

Quest Diagnostics is always working to improve our assay. Since the test launch in 2015, we have made multiple updates to improve the assay and the experience of our patients. In the last 2 years, we have optimized the assay to allow us to request only 1 blood tube instead of 2, making the draw process easier for our patients. We also validated and launched our FF enrichment process, which selectively filters placental cfDNA fragments from a sample. The process increases the relative FF and reduces the number of cases with FF values too low for analysis.