FISH, Prenatal Aneuploidy Detection- Fetal Cord Blood (5 Probes-Trisomy 21,18,13;X,Y)

About this test

This assay is intended to identify substantial copy number differences affecting chromosomes 21, 18, 13, X, and Y, which are frequently additional or missing chromosomes (i.e. aneuploidies). This test will not identify copy number variants that do not include the genomic region where the probe targets are located. Even though copy number increases and decreases are typically considered to affect the entire target chromosome, it's possible that the aberration is actually a partial aneuploidy or microdeletion/microduplication. When mosiasm of at least 6% is identified, the standard FISH investigation of 50 interphrase cells per chromosome/probe is enlarged to 100–200 cells.

A follow-up amniocentesis may be advised, especially in the absence of ultrasound abnormalities, for CVS specimens where a positive FISH test does not always mean that the foetus is damaged. A normal FISH outcome does not, in addition, rule out a chromosomal issue in the foetus. Chromosome analysis and/or chromosomal microarray should always be ordered in conjunction with prenatal FISH confirmation (CMA).

FISH – chromosomes 21, 18, 13, X, Y

Patients choosing diagnostic procedures (CVS, amniocentesis) as well as those in the postnatal context when aneuploidy is suspected can use Insight's quick fluorescence in situ hybridation (FISH) test to identify common aneuploidies of chromosomes 13, 18, 21, X, and Y. Our laboratory staff is extremely skilled in the identification of mosaic cell lines, and we provide enlarged cell counts to improve reporting accuracy and give clinicians and their patients more details. Ordering prenatal FISH together with chromosome analysis or chromosomal microarray is always recommended (CMA).

Turnaround time

Next business day

Accepted specimens

Amniotic fluid: 4+ mL for pregnancies under 18 weeks; 2+ mL for pregnancies over 18 weeks

CVS: collected in transport media, 3-5+ mg of villi

Blood was collected in a green top (sodium heparin) tube containing 0.3–0.5 mL of whole blood.

*All CVS, AF, and cord blood specimens must be accompanied by a maternal purple top (EDTA) blood or saliva sample.

FISH (experimented on fresh tissue or paraffin blocks)

There are numerous types of probes. It is helpful for identifying aneuploid diseases (trisomies, monosomies).

Although working with fixed tissues stored in paraffin blocks takes much more time and might be challenging, the approach can also be used on fixed tissues that have been stored in fresh cells. When karyotyping was not done or cells did not develop in culture, archival tissues can still be studied thanks to the ability to apply FISH on paraffin blocks.

DNA Probes

DNA sequences can be examined in foetal cells collected during amniocentesis or CVS. In some cases, a situation can be determined using the polymerase chain reaction (PCR) method if the DNA sequence of an allele is known and a probe to a DNA sequence.

There are many different types of birth defects, but only in a small percentage of them have specific genes been found, and in certain cases techniques to find them have been devised. As a result, not every birth problem can be linked to a particular genetic mutation. Additionally, the possibility of multiple mutations occurring in the same gene complicates testing, adding to its complexity.