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QNatal® Advanced

Test code(s) 92777

Question 1. How is the QNatal® Advanced test performed?

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 and select microdeletion regions are calculated.

Question 2. What does the QNatal Advanced test detect?

The QNatal Advanced test can detect the most common autosomal fetal abnormalities: trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome). It can also detect abnormalities of the sex chromosomes. These include Turner syndrome (monosomy X) and Klinefelter syndrome (XXY) as well as XXX and XYY syndromes. In addition, QNatal Advanced can detect 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).

Question 3. Can the QNatal Advanced test help determine the fetal sex?

Yes, the QNatal Advanced test can help determine fetal sex based on the presence or absence of cfDNA from the Y chromosome. However, if the clinician and patient do not wish to know the fetal sex, the healthcare provider can opt out of having it reported.

Question 4. Are positive results from the QNatal Advanced test diagnostic?

No. Like all noninvasive cfDNA prenatal screening tests, the QNatal Advanced test does not provide a diagnostic result. If the QNatal Advanced test yields a positive result for fetal aneuploidy, a follow-up diagnostic procedure such as chorionic villus sampling (CVS) or amniocentesis should be considered for definitive confirmation.

Question 5. Which disorders are not detected by the QNatal Advanced test?

The QNatal Advanced test does not detect copynumber 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 cfDNA prenatal screening tests, the QNatal Advanced test cannot identify nonsyndromic congenital anomalies (ie, birth defects). For example, it cannot detect a neural tube defect.

Question 6. When should the QNatal Advanced test be considered for a patient?

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 or diagnostic testing for fetal genetic disorders, regardless of maternal age.1 The American College of Medical Genetics and Genomics (ACMG) states that there is strong evidence that noninvasive prenatal screening can replace conventional screening for trisomies 13, 18, and 21, regardless of maternal age.2

A published clinical study3 on the performance of the QNatal Advanced test in a population of pregnant women that included both those at average and those at high risk demonstrated excellent analytical sensitivity and specificity for trisomy 21, 18, and 31. 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, and 75.0% for microdeletions. Overall, the PPV for fetal aneuploidies was 87.2%; sensitivity was 97.9% and specificity was 99.9%.

Question 7. When would the QNatal Advanced test not be considered for a patient?

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

Question 8. Can the QNatal Advanced test be performed on specimens from a multiple-gestation pregnancy or a pregnancy with a donor ovum?

Yes, the QNatal Advanced test can be performed on specimens from both of these types of pregnancy.

Question 9. How reliable are noninvasive cfDNA prenatal screening tests?

Noninvasive cfDNA-based prenatal screening tests have been shown to be very reliable in validation studies.4-6

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.

Question 10. What is the turnaround time for the QNatal Advanced test?

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).

Question 11. What is included in the QNatal Advanced test report?

The report includes a “negative” or “positive” result for trisomy 21, 18, and 13. Sex-chromosome abnormalities and microdeletion syndromes will be reported as “increased risk” (unless microdeletion testing has been opted out). Fetal sex is reported as well, if not opted out.

Question 12. When might I not receive a result?

Some specimens do not contain enough fetal cfDNA (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.

Question 13. What is the follow up after a QNatal Advanced test?

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.7

Implications of a positive or increased risk result should be discussed with the patient. Diagnostic confirmation using amniocentesis or CVS should be offered.7

References

  1. Committee on Practice Bulletins—Obstetrics, Committee on Genetics, and the Society for Maternal-Fetal Medicine (2016). Practice Bulletin No. 163: Screening for Fetal Aneuploidy. Obstet Gynecol. 2016;127(5):e123-e137. doi: 10.1097/AOG.0000000000001406
  2. Gregg AR, Skotko BG, Beckendorf, J, et al.  Noninvasive prenatal screening for fetal aneuploidy, 2016 update: a position statement of the American College of Medical Genetics and Genomics. Genet Med. 2016;18:1056-1065. doi: 10.1038/gim.2016.97
  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:e545. doi: 10.1002/mgg3.545. Epub 2019 Jan 31.
  4. Committee Opinion No. 640: Cell-free DNA screening for fetal aneuploidy. Obstet Gynecol. 2015;126:e31-e37.
  5. Quest Diagnostics. Data on file.
  6. 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.
  7. Committee opinion no. 640: cell-free DNA screening for fetal aneuploidy. Obstet Gynecol. 2015;126:e31-e37.
This FAQ is provided for informational purposes only and is not intended as medical advice. A clinician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.
Document FAQS.167 Version: 1
Version 1: Effective 12/19/2019 o present
Version 0: Effective 10/28/2015 to 12/19/2019