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Microarray (prenatal)

Also known as: Prenatal SNP array, amniotic fluid microarray testing, CVS microarray testing, SNP microarray, CGH microarray, CGH array

Test category:

Reproductive - Fetal diagnosis

Use of test

Purpose:

 Microarray analysis can detect submicroscopic deletions and duplications of genetic material across all chromosomes. It provides a higher resolution analysis than a karyotype study, but doesn't provide positional information e.g. genetically balanced rearrangements.

Microarray (rather than karyotype) is usually the recommended investigation for prenatal studies. However, microarray is usually not the preferred test to confirm a finding of aneuploidy on non-invasive prenatal testing as it cannot differentiate free aneuploidy from aneuploidy due to a parental translocation; a karyotype would usually be recommended to Karyotype (CVS).

Utility:

The presence of a pathogenic abnormality provides specific diagnostic and prognostic information. Further family studies may clarify the recurrence risk in relatives.

The absence of a pathogenic abnormality does not necessarily exclude a clinical diagnosis.

Microarrays can also detect deletions and duplications that are of unknown clinical significance or which have variable clinical outcomes ('susceptibility variants') . Rarely, deletions or duplications which are associated with a clinically significant disorder unrelated to the presentation of the patient may be detected. The report will provide advice regarding the interpretation of such findings.

Ethical considerations:

This is an assay for mutations which may be heritable or de novo. It may raise issues of ethics or consent that are different from most other investigations ordered in the routine care of a patient. Use of the consent form (below) is not mandated, but could be used to guide the discussion with the patient.

Consent form:

Download the Sonic Genetics consent form.

Methodology:

The relative amounts of genetic material from hundreds of thousands of small regions from all chromosomes are measured. Deviations from the expected values can identify deletions and duplications.

Sonic Genetics uses a single nucleotide polymorphism (SNP) microarray, which provides additional genotype information compared with CGH microarray. SNP microarrays can identify large regions of homozygosity, which may be useful in detecting uniparental disomy or an increased likelihood of a recessive disorder.

Requesting the test

Ordering:

This test is usually requested by an obstetrician or clinical geneticist. A prenatal FISH test is usually also requested to provide a fast initial exclusion of the major trisomies.

Sample required:

Chorionic villus or amniotic fluid sample is required. An invasive procedure by an obstetrician is necessary to obtain this.

To help ensure the quality of the test, a genetic test should be done with a dedicated sample whenever possible i.e. a sample collected specifically for that test rather than a sample that is used for multiple tests.

We recommend that the patient or another adult check the labelling of request forms and sample containers.

Special instructions:

Please include details of any clinical abnormalities in the patient being tested, and the results of chromosome or array studies in relatives.

Turnaround time:

15 days (1-2 days for FISH).

Price:

This test has a Medicare rebate which, subject to the requirements of the Medicare descriptor being met, may cover all or part of the cost.

Note that microarray and karyotype analyses cannot both be rebated on the same test episode.

This investigation is provided at no additional out of pocket cost for patients qualifying for a Medicare rebate following a "high risk" result for the Harmony test through Sonic Genetics.

Rebate:

The Medicare details, including descriptor and schedule fee, are listed under MBS item 73287.