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Quest Diagnostics

QNatal® Advanced

Test code(s) 92777

The QNatal Advanced test is performed on cell-free DNA (cfDNA) isolated from maternal blood. This cfDNA contains both maternal DNA and fetal DNA derived from apoptotic placental cells (trophoblasts). Once isolated, the cfDNA is sequenced using massively parallel shotgun sequencing (MPSS); this is followed by quantitative bioinformatics analysis. In this way, the fetal copy number of chromosomes 21, 18, 13, X, Y, as well as select microdeletion regions, are calculated.

QNatal Advanced screens for the most common autosomal fetal abnormalities: trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome). It can also screen for abnormalities of the sex chromosomes. These include Turner syndrome (monosomy X) and Klinefelter syndrome (XXY) as well as XXX and XYY syndromes. In addition, if elected, QNatal Advanced can screen for microdeletions that are too small to be detected by standard cytogenetic analysis. These include microdeletions of chromosomes 1p (1p36 syndrome), 4p (Wolf-Hirschhorn syndrome), 5p (Cri-du-chat syndrome), 8q (Langer-Giedion syndrome), 11q (Jacobsen syndrome), 15q (Prader-Willi/Angelman syndromes), and 22q (DiGeorge syndrome).  

Yes, if elected, the QNatal Advanced test can screen for fetal sex based on the presence or absence of cell-free DNA from the Y chromosome. However, if the patient does not wish to know the fetal sex, the healthcare provider can opt out of having it reported.

No. Like all noninvasive cell-free DNA prenatal screening tests, the QNatal Advanced test does not provide a diagnostic result.* If the QNatal Advanced test yields a result of positive for increased risk, the patient should receive genetic counseling and further diagnostic testing and procedures, when clinically indicated.

Pregnancy management decisions should not be based on the results of a cell-free DNA test alone. 

The QNatal Advanced test does not detect copy number abnormalities of chromosomes other than 21, 18, 13, X, or Y, or abnormalities involving only a portion of a chromosome outside the microdeletion regions of interest. Additionally, like other noninvasive cell-free DNA prenatal screening tests, the QNatal Advanced test cannot identify nonsyndromic congenital anomalies (ie, birth defects). For example, it cannot detect a neural tube defect or a ventral wall defect.

This test can be used for all pregnant women. The American College of Obstetricians and Gynecologists (ACOG) and the Society of Maternal-Fetal Medicine (SMFM) recommend that all women should be offered the option of aneuploidy screening (ie, screening for the trisomies and sex chromosome abnormalities) or diagnostic testing, regardless of maternal age.1 The American College of Medical Genetics and Genomics (ACMG) states that noninvasive prenatal cell-free DNA screening is “the most effective screening test” for trisomies 13, 18, and 21 “in singleton and twin gestations.”2

A published clinical study3 examined the performance of the QNatal Advanced test in a population of pregnant women that included both those at average and those at high risk. The results demonstrated strong analytical sensitivity and specificity for trisomy 21, 18, and 13. The positive predictive value (PPV) was 98.1% for trisomy 21, 88.2% for trisomy 18, 59.3% for trisomy 13, 69.0% for sex-chromosome aneuploidies (ie, 45,X; 47,XXY; 47,XXX; and 47,XYY in the aggregate), and 75.0% for microdeletions (ie, 22q; 5p; 1p36; 15q; 11q; 8q; and 4p in the aggregate).* 

Testing should not be performed prior to 10 weeks gestational age.

Yes, the QNatal Advanced test can be performed on specimens from twin gestations.4

Noninvasive cell-free DNA-based prenatal screening tests have been shown to be very reliable in validation/verification3,4 and real-world studies.2

False-positive and false-negative results do occur; causes include, but are not limited to, confined placental mosaicism, co-twin demise/vanishing twin, fetal mosaicism, maternal mosaicism, possible fibroids, and maternal malignancy.

Table showing sensitivity and specificity for non-invasive cell-free DNA prenatal screening tests. Click the table to enlarge.

Results are typically reported within 5 to 7 days after specimen collection. Results are sent to the ordering healthcare provider’s office or to the electronic medical record (EMR).

The report includes a “negative” or “positive” result for trisomy 21, 18, and 13.  All positive results for trisomies include age-adjusted positive predictive value (PPV). Sex-chromosome abnormalities and microdeletion syndromes are reported as “increased risk” (unless microdeletion testing has been opted out). Fetal sex is reported as well, if not opted out.

Some specimens do not contain enough fetal cell-free DNA (fetal fraction). If this happens, test results cannot be obtained, interpreted, or reported. Low fetal fraction can be due to several factors, including, but not limited to, maternal obesity. The test can be repeated using newly collected maternal blood specimens. If no result is obtained on the second specimen, consideration of a diagnostic test may be appropriate.

No specific follow-up is needed when the test is negative.* However, if ultrasound examination of the fetus reveals anomalies, then further fetal studies might be indicated.

Implications of a positive or increased risk result should be discussed by the healthcare provider with the patient. Diagnostic confirmation using amniocentesis or chorionic villus sampling should be offered.1

References

  1. American College of Obstetricians and Gynecologists’ Committee on Practice Bulletins—Obstetrics, Committee on Genetics, Society for Maternal-Fetal Medicine. Screening for Fetal Chromosomal Abnormalities: ACOG Practice Bulletin, Number 226. Obstet Gynecol. 2020;136(4):e48-e69. doi:10.1097/AOG.0000000000004084 
  2. Rose NC, Barrie ES, Malinowski J, et al. Systematic evidence-based review: The application of noninvasive prenatal screening using cell-free DNA in general-risk pregnancies. Genet Med. 2022; 24(7):1379-1391. doi:10.1016/j.gim.2022.03.019
  3. Guy C, Haji-Sheikhi F, Rowland CM, et al. Prenatal cell-free DNA screening for fetal aneuploidy in pregnant women at average or high risk: results from a large US clinical laboratory. Mol Genet Genomic Med. 2019;7(3):e545. doi:10.1002/mgg3.545 (Some authors affiliated with Quest Diagnostics)
  4. Anderson B, Zhang K, Nguyen Q, et al. An automated, non-invasive prenatal screening assay (NIPS) for trisomy 21, 18, 13 in singleton and twin gestations. Int J Gynaecol Obstet. 2015;131(Suppl 5):E264. (Some authors affiliated with Quest Diagnostics)

 

 

* QNatal® Advanced is a cell-free DNA test that screens for increased risk of certain fetal chromosomal abnormalities that may cause birth defects, including Trisomy 21 (Down Syndrome), Trisomy 18, Trisomy 13, and certain sex chromosome abnormalities (ie, 45,X; 47,XXY; 47,XXX; and 47,XYY). In addition, if selected as an option, QNatal Advanced can screen for certain microdeletions (ie, 22q; 5p; 1p36; 15q; 11q; 8q; and 4p) that may cause birth defects, and/or for fetal sex. This test does not assess the risk of fetal anomalies such as neural tube defects or ventral wall defects. QNatal Advanced is not recommended before 10 weeks gestation due to a significantly increased risk of a failed result.

QNatal is a “screening” test, not a diagnostic test; therefore, all positive for increased risk results should be followed by genetic counseling and further diagnostic testing and procedures, when clinically indicated. Pregnancy management decisions should not be based on the results of a cfDNA test alone. As with any test, false-positive or false-negative results do occur. The positive predictive value of the screening test varies by genetic marker and may be lower for rare conditions. Performance data for the QNatal Advanced may be obtained by contacting Quest Diagnostics at 1.866.GENE.INFO (1.866.436.3463).

 

QNatal Advanced is a laboratory-developed test that has been developed and validated pursuant to the Clinical Laboratory Improvements Amendments of 1988 (CLIA), and as such it has not been reviewed by FDA.

 


This FAQ is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on the physician’s education, clinical expertise, and assessment of the patient.

 

Document FAQS.167 Version: 2
Version 2: Effective 05/09/2023 to present

Version 1: Effective 12/19/2019 to 05/09/2023

Version 0: Effective 10/28/2015 to 12/19/2019

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