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Chromosome Analysis, Chorionic Villus Sample

Test code(s) 14592X

Question 1. Multiple fetal anomalies were detected on ultrasound, but the chromosome analysis was normal. Are there further genetic studies that can be done to evaluate the fetal anomalies?

Yes, there are other studies that may be appropriate. There are many causes of fetal anomalies, some of which are genetic. In the absence of clinical suspicion for a specific genetic disorder, a microarray analysis may be performed on the chorionic villus sample to detect subtle deletions and duplications (Chromosomal Microarray, Prenatal, ClariSure® Oligo-SNP [test code 90927]). If clinical suspicion exists for a specific disorder, there may be other genetic testing available. Please contact Quest Genomics Client Services at 866-GENE-INFO to discuss the case with a genetic counselor and for information on adding another test.

Question 2. My patient has a personal or family history of a chromosome abnormality. Prenatal chromosome analysis was reported as normal. Does this result guarantee the fetus doesn’t have the familial chromosome abnormality?

No, please call Quest Genomics Client Services at 866-GENE-INFO to discuss this case with a genetic counselor. Documentation of the specific genetic abnormality in the family will be necessary to determine the accuracy of the testing that was performed on the fetus.

Question 3. Which chromosome abnormalities does this assay rule out?

This assay rules out:

  • Trisomies such as Down syndrome, trisomy 18, and trisomy 13
  • Sex chromosome abnormalities such as Turner syndrome and Klinefelter syndrome
  • Most rearrangements, including Robertsonian translocations and inversions
  • Marker chromosomes
  • Mosaicism above 14% (at a 95% confidence level); if mosaicism is suspected please call Quest Genomics Client Services at 866-GENE-INFO to discuss this case with a genetic counselor prior to sending the specimen to best assure that the correct tests are ordered.

Question 4. Which disorders cannot be detected by this assay?

This assay cannot detect:

  • Most microdeletion syndromes, including DiGeorge, Prader-Willi, Angelman, Williams, and Smith Magenis
  • Mosaicism below 14% (at a 95% confidence level)
  • Fragile X syndrome
  • Single gene disorders such as cystic fibrosis, Marfan syndrome, neurofibromatosis, etc.
  • Disorders associated with small cryptic (not microscopically visible) gains or losses or genetic material

If a microdeletion syndrome or mosaicism is suspected, please call Quest Genomics Client Services at 866-GENE-INFO to discuss this case with a genetic counselor prior to sending the specimen to best assure that the correct tests are ordered.

Question 5. The report indicates that maternal cell contamination (MCC) cannot be ruled out. Is there a test that can be done to evaluate for MCC?

Yes. Maternal Cell Contamination Study, STR Analysis (test code 10262) can be used to test for maternal cell contamination. A maternal blood specimen is needed for this test. Ideally, the maternal specimen would be submitted with the prenatal specimen. If you are considering adding this test to a completed prenatal case, please call Quest Genomics Client Services at 866-GENE-INFO to speak with a genetic counselor. 

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 his/her education, clinical expertise, and assessment of the patient.
Document FAQS.76 Version: 1
Version 1 effective 05/21/2015 to present
Version 0 effective 9/12/2012 to 05/20/2015