FISH - Prenatal

The ACMG & ASHG issued a joint position statement on FISH “For management of the fetus, it is reasonable to report positive FISH test results. Clinical decision-making should be based on information from two of three of the following: positive FISH results, confirmatory chromosome analysis, or consistent clinical information.”1

FISH (Fluorescence In -Situ Hybridization) is a cytogenetic test for common chromosomal abnormalities such as Trisomy 13, Trisomy 18, Trisomy 21. In this technique, a Specific fluorescent dye coupled to a probe complementary to a particular chromosome region. FISH targets only limited regions of the genome

Clinical utility

  • FISH is highly effective in detecting common chromosomal aneuploidies,
  • FISH offers a quick turnaround time, allowing for timely decision-making in prenatal care.
  • Targeted Analysis: FISH is a targeted test that focuses on specific chromosomal regions.
  • FISH results can guide further diagnostic testing, such as chromosomal microarray analysis (CMA) or karyotyping, to obtain a comprehensive assessment of the fetal chromosomal profile.

When is it recommended

  • Iin cases with a high risk or suspicion of specific chromosomal aneuploidies .
  • When rapid results are needed, allowing for timely decision-making in pregnancy management.
  • FISH is particularly valuable for targeted investigation of specific chromosomal abnormalities associated with known microdeletion/microduplication syndromes or chromosomal rearrangements.

Test specification

Technique Variant types TAT Sample requirements
FISH AS + SV 6 - 7 days Amniotic Fluid, CVS(chorionic villus sample)



  1. Test and Technology Transfer Committee. Technical and clinical assessment of fluorescence in situ hybridization: an ACMG/ASHG position statement. I. Technical considerations. Genet Med. 2000 Nov-Dec; 2(6): 356-61.


Are there any limitations or drawbacks to FISH in prenatal testing?

FISH is a targeted test that focuses on specific chromosomal regions, which means it can only detect the abnormalities it is designed to identify. It may not detect all chromosomal abnormalities or gene-level mutations. If additional abnormalities are suspected, further genetic testing may be required.

Is FISH a definitive diagnostic test in prenatal testing

Is FISH considered a safe procedure for prenatal testing?

Can FISH be performed on all pregnancies?