Our prenatal cytogenetic tests provide diagnostic answers in pregnancy including after high risk results from screening tests

Prenatal diagnosis of chromosomal abnormalities in fetuses, and investigation of genetic causes for pregnancy loss can be tested through a number of cytogenetic techniques. This includes conventional chromosome studies (karyotyping), chromosomal microarray (molecular karyotyping), and fluorescence in situ hybridisation. 

Depending on the stage of the pregnancy, different sample types may need be tested. Cytogenetic investigations may be indicated to confirm high risk NIPT or first trimester screen results, or where structural anomalies of the fetus are detected by ultrasonographic examination. 

Methods

Conventional Chromosome analysis has long been the gold standard for detecting cytogenetic abnormalities in foetuses for prenatal diagnosis and pregnancy loss. These studies involve the analysis of the whole genome at the cellular level to detect large genomic changes and chromosomal rearrangements and readily identify whole chromosome aneuploidy (gain or loss) and chromosomal rearrangements (balanced or large unbalanced). It is applicable where the primary clinical or test result indications are syndromes such as Down syndrome or Turner Syndrome.

This test involves culturing white blood cells to produce metaphase spreads of chromosomes, from which slides are prepared and representative cells are captured into digital images.

Recent studies in high risk prenatal diagnosis have shown that cytogenetic investigation by chromosomal microarray (also known as molecular karyotyping) has an improved detection rate of pathogenic abnormalities as they allow the detections of chromosomal deletions and duplications at much higher resolutions.

The molecular karyotype will provide information about the genes involved in the regions of copy number alteration and can detect common causes of pregnancy loss, such as whole or partial chromosome aneuploidy, triploidy and molar pregnancies. The information provided will assist in the management of patients with recurrent pregnancy loss.

Fluorescence in-situ hybridisation (FISH) is a targeted molecular cytogenetic technique used for the investigation of precise chromosome regions, particularly relevant when a specific condition is suspected. The technique binds a colour labelled DNA probe to a specific region on the patient chromosomes.

As this is a targeted test it is important when requesting a FISH test to indicate the clinical condition that is being tested for.

Sample Types

Test NameChromosomes Analysis on CVSFISH on CVS
Clinical IndicationPrenatal diagnosis in patients with indications of a high-risk pregnancyFor prenatal diagnosis of suspected chromosomal syndromes
Gene(s)All chromosomes13, 18, 21 and X and Y chromosomes
MethodConventional Chromosome analysis OR Microarray analysisFISH for 13, 18, 21, X and Y chromosomes
Turn Around Time10-12 days1 day
Medicare Eligibility73287No
Sample Type10-30mg Chorionic villus sample (Doctor collect)
Collection TypeSterile 10ml tube
Special InstructionsDoctor collect only. Both tests performed on each sample.
Test NameChromosomes Amniotic FluidFISH on Amniotic fluid
Clinical IndicationPrenatal diagnosis in patients with indications of a high-risk pregnancyFor prenatal diagnosis of suspected chromosomal syndromes
Gene(s)All chromosomes13, 18, 21 and X and Y chromosomes
MethodConventional Chromosome analysis OR Microarray analysisFISH 13, 18, 21, X and Y chromosomes
Turn Around Time10-12 days1 day
Medicare Eligibility73287No
Sample Type2 x 9mL amniotic fluid (Doctor collect)
Collection TypeSterile 10mL tube x 2
Special InstructionsDoctor collect only. DO NOT SEPARATE TUBES, SEND ALL TUBES TO YOUR LOCAL LABORATORY IMMEDIATELY. For overnight transport, the sample should be cooled NOT FROZEN. Both methods performed on each sample.
Test NameChromosomes Products of Conception (POC)
Clinical IndicationFor the investigation of chromosomal causes for miscarriage and pregnancy loss
Gene(s)All chromosomes
MethodChromosome Microarray
Turn around time18 days
Medicare Eligibility73287
Sample TypeProducts of Conception, Foetal Tissue & Skin (Doctor Collect)
Collection TypeSterile container with Antibiotic Transport Media/ Saline
Special InstructionsSample must be kept sterile and moist. DO NOT USE FORMALIN. USE ANTIBIOTIC TRANSPORT MEDIA available from the Histology Department of your local laboratory. For overnight transport cover large specimens with ANTIBIOTIC TRANSPORT MEDIA OR STERILE NORMAL SALINE and sent to your local laboratory IMMEDIATELY. Please indicate if the specimen is to be shared with Histology.

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