Amniotic Fluid, Chorionic Villus Sampling (Prenatal) — FISH Analysis

CPT Code(s): 88235, 88275, 88271(x5)

Service Code (IU Health): 53101234, 53100707, 53100640

Ordering Recommendation: Detection of prenatal (fetal) aneuploidy (13, 18, 21, X, Y) in individuals with advanced maternal age (AMA), family history of genetic abnormality, abnormal prenatal screening, or abnormal fetal ultrasound. Assay offered in conjunction with chromosome study. No additional specimen required.

Synonyms: FISH, prenatal aneuploidy, trisomy, prenatal chromosomes.

Methodology: Fluorescence in situ hybridization (FISH) analysis.

Performed: Monday through Friday

Reported: 2 days

Patient Preparation: 14 weeks gestation or greater (or alternatively 1 mL/week of gestation for amniocentesis between 12 and 14 weeks) in a sterile syringe). 

Collect: Discard first 2-3 mL to avoid maternal cell contamination. Place remaining fluid in 3-4 aliquots, labeled 1st, 2nd, etc in sterile tubes. Sterile Corning centrifuge tubes can be provided upon request.

Specimen Volume: 10-25 mL amniotic fluid.

Storage/Transport: Refrigerate. Do not centrifuge.

Unacceptable Conditions: Frozen. Centrifuged.

Remarks: For bloody specimens, use centrifuge tubes containing sodium heparin (can be provided). 

Stability: Ambient: 24 hours; Refrigerated: 48 hours; Frozen: Unacceptable

Characteristics:

Negative: Individuals with 2 signals for a probe exhibit a normal signal pattern and are considered negative for a loss/gain of the chromosome tested by the probe.

Positive: Individuals with a FISH signal pattern indicating loss/gain of a chromosome signal tested by the probe panel. The normal range varies with each observed signal pattern and is listed in the table below. A report detailing interpretation of results will be provided.  Genetic counseling is recommended for individuals with abnormal results.

Reference Range:

Limitations: This analysis does not eliminate the possibility of low frequency mosaicism or small structural abnormalities.