Also known as: Chromosome studies, karyotype (prenatal)
Reproductive - Fetal diagnosis
Use of test
Chromosome analysis can detect balanced and unbalanced rearrangements, and numerical changes of autosomes and sex chromosomes. Chromosome studies of the parents may be necessary to clarify the genetic diagnosis and the risks to fetus. Prenatal microarray study is usually a more appropriate test than karyotype as submicroscopic deletions can be detected. A karyotype can be performed in certain situations, or on request. In particular, karyotype (not microarray) is recommended following an abnormal non-invasive prenatal screening test for aneuploidy as it can detect both standard aneuploidy and aneuploidy due to a parental translocation.
An abnormal result usually provides a genetic diagnosis and the basis for genetic counselling. A normal result does not exclude a genetic or heritable abnormality as submicroscopic changes would not be detected.
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.
Analysis of metaphase chromosomes by light microscopy. Chromosomes are counted, and examined for structural and numerical abnormalities.
Requesting the test
This test is usually requested by an obstetrician or clinical geneticist.
Chorionic villus 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.
Rapid prenatal FISH is also available for rapid detection of specific abnormalities. Rapid FISH does not replace the need for comprehensive karyotype.
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.
This investigation is provided at no additional out of pocket cost for patients qualifying for a Medicare rebate following a "high risk" result with the non-invasive prenatal test (NIPT) through Sonic Genetics.
The Medicare details, including descriptor and schedule fee, are listed under MBS item 73287.