Chromosome Analysis – Amniotic Fluid
Also known as: Karyotype
Use
Chromosome analysis of amniotic fluid is clinically relevant for detection of fetal chromosomal numerical and structural abnormalities, including common trisomies such as trisomy 21 (Down syndrome), trisomy 18, trisomy 13, sex chromosome aneuploidies (e.g., Turner syndrome 45,X; Klinefelter 47,XXY), Robertsonian translocations, inversions, marker chromosomes, mosaicism ≥ 14% (95% confidence), and most visibly detectable structural abnormalities.
Special Instructions
Physicians may consider additional testing if aneuploidy is not detected but clinical suspicion remains, including chromosomal microarray analysis (e.g., ClariSure Oligo‑SNP CMA, test code 90927). Maternal cell contamination may require STR Analysis (test code 10262). Consultation with Quest Genomics Client Services at 866‑GENE‑INFO is recommended for complex cases or additional test additions.
Limitations
This assay cannot detect subtle rearrangements, microduplications, microdeletions (e.g., DiGeorge, Prader‑Willi, Angelman, Williams, Smith‑Magenis syndromes), low‑level mosaicism below 14% (95% confidence), single‑gene disorders (e.g., fragile X, cystic fibrosis, Marfan syndrome, neurofibromatosis), neural tube defects, or other birth defects associated with elevated maternal serum alpha‑fetoprotein. Maternal cell contamination cannot always be ruled out and may require additional testing.
Methodology
Chromosomal / Cytogenetics (Karyotype)
Biomarkers
Result Turnaround Time
7-10 days
Related Documents
For more information, please review the documents below
Specimen
Body Fluid
Volume
10‑25 ml (optimal 20‑25 ml) amniotic fluid
Minimum Volume
10 ml
Container
sterile leak‑proof conical tubes (e.g., two 15 ml tubes); discard first 1 ml to avoid maternal cell contamination
Collection Instructions
Amniotic fluid; discard first 1 ml (or first 2–3 ml per alternate sources) to avoid maternal cell contamination; place remaining fluid into 3–4 sterile aliquots
Storage Instructions
Room temperature; do not refrigerate or freeze; transport promptly
Causes for Rejection
Frozen sample; refrigerated sample; failure to discard initial fluid; clotted or otherwise compromised sample
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | approx. 8 h (then refrigerate not recommended) |
| Frozen | Unacceptable |