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Chromosome Analysis, Amniotic Fluid

Test code(s) 14590X

Question 1. Multiple fetal anomalies were detected by ultrasound in this pregnancy, but chromosome analysis was normal. Are there further studies that can be done to evaluate for a genetic disorder in the fetus?

Yes, there are other studies that may be appropriate. There are many causes for fetal anomalies, some of which are genetic. In the absence of clinical suspicion for a specific genetic disorder, a microarray analysis may be performed 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 additional testing.

Question 2. My patient has a personal or family history of a chromosome abnormality. Prenatal chromosome testing on the fetus was reported as normal. Does this result guarantee that the fetus has not inherited the abnormality?

No. Please call Quest Genomics Client Services at 866-GENE-INFO to discuss this case with a genetic counselor. We need to know the specific genetic abnormality in the family, so we can determine whether the test’s resolution was sufficient to detect the abnormality.

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

This assay can rule out:

  1. Trisomies such as trisomy 21 (Down syndrome), trisomy 18, and trisomy 13
  2. Sex chromosome abnormalities such as Turner syndrome (45,X) and Klinefelter syndrome (47,XXY)
  3. Most rearrangements, including Robertsonian translocations and inversions
  4. Marker chromosomes
  5. Mosaicism at or above 14% (at a 95% confidence level)
  6. Most microscopically visible structural abnormalities

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

This assay cannot detect:

  1. Subtle rearrangements, microduplications, and most microdeletion syndromes, including DiGeorge, Prader-Willi, Angelman, Williams, and Smith-Magenis syndromes
  2. Mosaicism below 14% (at a 95% confidence level)
  3. Single gene disorders such as fragile X syndrome, cystic fibrosis, Marfan syndrome, neurofibromatosis, etc.

Nor can this assay detect neural tube defects, abdominal wall defects, or other birth defects associated with an elevated maternal serum alpha-fetoprotein. If you wish to test for these defects consider ordering Alpha-Fetoprotein, Amniotic Fluid with Reflex to AchE and Fetal Hgb (test code 232Z). Please contact Quest Genomics Client Services at 866-GENE-INFO for information on adding this test to a prenatal sample. 

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

Yes. The Maternal Cell Contamination Study, STR Analysis test (test code 10262X [10477X for NY]) can be performed if a maternal blood sample is submitted. If you are considering adding MCC studies 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.48 Version: 3
 
Version 3 effective 04/19/2016 to present
Version 2 effective 06/26/2014 to 04/18/2016
Version 1 effective 11/19/2012 to 06/25/2014
Version 0 effective 04/20/2011 to 11/18/2012