FISH - Postnatal

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

  • Confirmation of Prenatal Testing Results: If a specific chromosomal abnormality was identified during prenatal testing, FISH can be employed to reconfirm the finding and provide additional evidence.
  • Rapid diagnosis of certain genetic conditions caused by specific chromosomal abnormalities.
  • FISH allows for targeted analysis of relevant genetic regions, aiding in the prompt identification of conditions such as microdeletion syndromes and other well-defined chromosomal abnormalities.
  • Tissue-Specific Analysis. This is particularly helpful in situations where a suspected genetic abnormality is limited to certain tissues or mosaicism is suspected, allowing for precise analysis and diagnosis.

When is it recommended

  • When the mother has a known chromosomal rearrangement
  • When there are concerns about genetic conditions that are specific to the baby
  • When there is a need to confirm or rule out specific chromosomal abnormalities that were detected through other diagnostic tests
  • In cases where rapid results are essential for immediate medical intervention or counseling

Test specification

Technique Variant types TAT Sample requirements
FISH AS + SV 6 - 7 days 3- 4 ml Blood in EDTA




  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.


When is FISH recommended in postnatal testing?

FISH is recommended in postnatal testing when there is a clinical suspicion of a specific genetic condition or chromosomal abnormality based on the individual's phenotype, family history, or other diagnostic findings. It is often employed for targeted analysis in cases where a particular chromosomal abnormality is suspected.

Can FISH provide a definitive diagnosis of a genetic condition?

Are there any limitations or drawbacks to FISH testing in postnatal analysis?