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Chromosome Analysis -Prenatal
Short Description : Chromosome Analysis-Prenatal


Chromosome Analysis
Test performed by: LabPLUS - Dept. Diagnostic Genetics - Cytogenetics


Results or General Enquiries : use ward computer or contact Lablink: ext 22000, DDI (09) 307-8995 or 0800 522 7587.

Other contacts: Section Leader: Philip Asquith ext 22008

Turnaround times  are according to the HGSA guidelines.

Amniotic fluid and Chorionic Villus samples :
Molecular Karyotype and conventional  G-banded karyotype results are available usually between 10-21 days, depending sample size, gestational age and  cell growth rate. 


Fetal blood samples :
G-banded karyotype results are available in 3-5 days.  Molecular karyotype results available in 14 days

See chromosome analysis Blood (constitutional) for more details.

Rapid FISH / Aneuscreen tests on prenatal samples (if requested): Results are usually available within  2 working days (see FISH section below for more details).

A range of molecular and Biochemical tests are also available prenatally. 

See Molecular Genetics, Molecular Haematology, and Biochemistry sections for more details.


Specimen Collection

All samples for Cytogenetics must be collected using sterile technique.
Same day delivery (at room temperature).

The laboratory must be informed that specimens are being sent:- Contact (See contact details)

Please complete all relevent boxes on the referral form, in order for correct processing of the sample.  Essential information includes:-

- Maternal Age (or Date of Birth),

- Gestational Age (or EDD),

- Previous Obstetric History,

- Any relevent clinical details / Ultrasound findings,

- Any further tests required.

If you require a request form please contact the laboratory, or for urgent cases please download and print the request form from the link below.

Download: - Laboratory Request Form Diagnostic Genetics__blank_copy_id_3256944.pdf

Diagnostic Genetics Request Form


Sterile Container18 mL Adult Sterile Container Amniotic Fluid

For Amniotic Fluid samples (AFs) :-  

18ml of fluid  at 16 weeks + gestation is the optimum size for molecular karyotype analysis, however smaller samples at earlier gestations can be processed but may incur an increased turnaround time.  Collect into a sterile 20 ml universal container (obtainable from the laboratory in an emergency). 


Sterile Container10 mg Adult Sterile Container Chorionic Villus

For Chorionic Villus samples (CVs) :-   

Ideally a minimum of 10-20 mg of tissue is the optimum size for molecular karyotype analysis, however smaller samples at earlier gestations can be processed but may incur an increased turnaround time. Samples should be collected aseptically into transport media. Transport media is supplied by the Cytogenetics Laboratory and should be stored in the refrigerator for no longer than three weeks (or six months if frozen) before being discarded.  



FISH
Test performed by: LabPLUS - Dept. Diagnostic Genetics - Cytogenetics


PRENATAL  ANEUSCREEN  (FISH)

NOTE: Other FISH or molecular tests for specific genetic conditions can be performed on prenatal specimens as required, please alert the laboratory on the request form if an additional test is required.

For results: use ward computer or phone Lablink: 22000 or (09) 307-8995 or 0800 522 7587.

Cytogenetic G-banded studies must be undertaken in addition to aneuscreen (FISH) analysis for prenatal diagnosis.

DIAGNOSTIC USE:
The locus specific probes used in this study - X centromeric, Y centromeric, 18 centromeric, 13q14 and 21q13-q22 will detect abnormalities only at the loci specified and will not detect other genetic alterations. Therefore the rapid prenatal FISH analysis will detect only 70 - 80% of all numerical chromosome abnormalities.  

For more information download the Aneuscreen leaflet from the link at the bottom of this page.

Also see Prenatal diagnosis - chromosomes


Specimen Collection

Please transport all specimens to the laboratory as soon as possible after collection. 

3mls of amniotic fluid are required for FISH testing alone, this is in addition to the 16 mls for karyotyping. 

Chorionic villus samples require an additional 1-2mg of  villi  for the FISH test.  There may not be sufficient material for this additional test in some small samples. 

Blood stained amniotic fluid specimens will NOT be accepted due to the high risk of maternal contamination.



DNA
Test performed by: LabPLUS - Dept. Diagnostic Genetics - Cytogenetics


Prenatal Array Studies

Molecular karyotype analysis (microarray) will be undertaken on all prenatal samples referred, with the exception of referrals where there is a history of a known familial chromosome rearrangement (ie balanced translocation)
Supporting clinical information (including ultrasound abnormalities) should be given on the referral form to aid karyotype analysis.


Turnaround Time: Between 2 weeks and 4 weeks


Molecular Karyotype- Prenatal Targeted

This approach uses the Affymetrix CytoScan 750k Cytogenetics array the which has a mean resolution of 100Mb Software thesholding allows the ability to detect small copy number variant within established deletion/duplication regions associated with pathogeneicity (see table below), The detection threshold outside these regions is 2Mb

1p36 deletion

15q24 deletion and duplication

2q37 deletion

16p13.3 deletion and   duplication

3q29 deletion

Miller Deiker/17p13.3 Duplication

Wolf Hirschhorn

HLPP/Charcot-Marie Tooth

Cri du Chat

Smith Magenis

Soto

17q11.2

Williams Beuren

Koolen De Vries

8p23.1

Cat Eye

Kleefstra

DiGeorge/Velocardiofacial/22q duplication

WAGR

Phelan McDermid

Potocki-Shaffer

Pelizaeus-Merzbacher

Angelman/Prader Willi

Rett

This is used to detect clinically significant copy number changes on referrals where no ultrasound abnormality has been observed.
Referral indications include:-
Positive maternal serum screening test (MSS)
Advanced maternal age (i.e. women over 35 years)
Maternal Anxiety
Family history of a genetic condition (NOT detectable by molecular karyotype or conventional cytogenetics)- Referred via Genetic Services
Previous live birth with a chromosome abnormality
Previous stillbirth with a potentially viable chromosome abnormality

 

Molecular Karyotype (Higher Resolution)
These will only be accepted via the NZ Maternal Fetal Medicine Network

This approach uses the Affymetrix CytoScan 750k Cytogenetics array which has a mean resolution of 100Mb and can detect small copy number variant across the entire genome
This is used to detect clinically significant copy number changes on referrals where an ultrasound abnormality has been observed.

Referral Indications include
Ultrasound scan showing abnormality
Nuchal Translucency 3.5mm or greater
Previous abnormal child with a copy number variant ascertained by microarray
History of the Genetic disorder (detectable by microarray analysis) ? Referrals via Genetic Services

Limitation

Microarray analysis will not detect balanced alterations, point mutations, imbalances of regions not represented on the microarray and may not detect low level mosaicism. Agenic regions, well established polymorphisms and regions only containing non-coding / pseudogenes are not reported. Male Y chromosome changes are not reported except in cases of suspected aneuploidy.  Regions of LOH (loss of heterozygosity) are only reported in cases indicative of whole chromosome UPD on chromosomes 7, 11, 14 or 15 or  cases where total autosomal LOH is >6%. Interpretation is based on GRCh37(hg19) human reference sequence.


Please refer to the Genetic Services 'Information sheet'.
Any queries contact Genetic Health Service NZ- Nothern Hub, on (64 09) 307-4949 ext 25870 or on 0800 476-123.

 

Conventional G-band Cytogenetic Analysis

This will be undertaken on referrals where a known familial chromosome rearrangement (ie balanced translocation)

Conventional G band cytogenetic results will also be issued in place of a molecular karyotype result  following an abnormal rapid aneuscreen  (FISH) report.

 


PRODUCTS OF CONCEPTION (POC)
See POC main page for more information.

 

 


Last updated at 17:14:02 05/12/2019