Prenatal Cytogenetic Tests

Chromosomal abnormalities in foetuses for prenatal diagnosis and investigation of pregnancy loss can be investigated through a number of cytogenetic techniques including conventional chromosome studies, chromosomal microarray and fluorescence in situ hybridisation. Dependant on the stage of the pregnancy, different sample types can be tested. Cytogenetic investigation may be indicated where there is a high risk NIPT results or first trimester screen, or where structural anomalies of the foetus are detected by ultrasonographic examination. The results are diagnostic.

 

 

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 Name

Chromosomes Analysis on CVS

FISH on CVS

Clinical Indication

Prenatal diagnosis in patients with indications of a high-risk pregnancy

For prenatal diagnosis of suspected chromosomal  syndromes

Gene(s)

Chromosomal Analysis

13, 18, 21 and X and Y chromosomes

Method

Conventional Chromosome analysis OR Microarray analysis

FISH 13, 18, 21, X and Y chromosomes

Turn Around Time

10-12 days

1 day

Medicare Eligibility

73287

No

Sample Type

10-30mg Chorionic villus sample (Doctor collect)

Collection Type

Sterile 10ml tube

Special Instructions

Doctor collect only. Both tests performed on each sample.

Test Name

Chromosomes Amniotic Fluid

FISH on Amniotic fluid

Clinical Indication

Prenatal diagnosis in patients with indications of a high-risk pregnancy

For prenatal diagnosis of suspected chromosomal  syndromes

Gene(s)

Chromosomal Analysis

13, 18, 21 and X and Y chromosomes

Method

Conventional Chromosome analysis OR Microarray analysis

FISH 13, 18, 21, X and Y chromosomes

Turn Around Time

10-12 days

1 day

Medicare Eligibility

73287

No

Sample Type

2 x 9mL amniotic fluid (Doctor collect)

Collection Type

Sterile 10mL tube x 2

Special Instructions

Doctor 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 Name

Chromosomes Products of Conception (POC)

Clinical Indication

For the investigation chromosomal causes for miscarriage and pregnancy loss

Gene(s)

Chromosomal Analysis

Method

Chromosome Microarray

Turn Around Time

18 days

Medicare Eligibility

73287

Sample Type

Products of Conception, Foetal Tissue & Skin (Doctor Collect)

Collection Type

Sterile container with Antibiotic Transport Media/ Saline

Special Instructions

Sample 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.

Test Name FISH Blood
Clinical Indication For neonatal diagnosis of suspected chromosomal syndromes
Gene(s) Chromosomes X and 21
Method FISH
Turn Around Time 2 days
Medicare Eligibility 73291
Sample Type Blood Paediatric Collect
Collection Type Minimum 1mL in 1 x Lithium heparin tube
Special Instructions No additional sample required. Test is performed with chromosome analysis