Cytogenetics (prenatal and fetal)

Last updated: Monday, 06, August, 2007

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Item Process
Specimen

Consult pathologist prior to specimen collection. All specimens must be delivered immediately to the laboratory.

Chorionic villus sampling (CVS): 5-15 mg of tissue in a sterile container with tissue culture medium.

Amniotic fluid: 20 mL of amniotic fluid collected into 2 x 10 mL sterile containers.

Foetal blood: 1-2 mL in sterile heparin tube.

If foetal death in utero has occurred: foetal tissue (especially cartilage or cord) collected aseptically and placed in sterile saline or tissue culture medium.

Method

Direct, short term and/or long term cultures are used depending on clinical requirements.

Results may take from 2 days to 3 weeks for completion. T

he type and duration of culture vary for the indication and specimen type.

Cytogenetic harvesting, slidemaking, banding and karyotyping are performed on all specimens.

Fluorescence in situ hybridisation (FISH) on metaphase spreads may increase the accuracy of cytogenetic diagnoses in some situations.
See also FISH.

Application

Pregnancies at risk include:
women of advanced maternal age;
those with a previous history of children with chromosome abnormalities;
parent with a known chromosome abnormality; and
those with a high risk identified by maternal serum screening.

Investigation is also appropriate if abnormalities are detected on ultrasound or identified after delivery and following unexplained stillbirth or neonatal death.

Interpretation

Findings are reported in terms of numerical and/or structural chromosome abnormalities (eg, deletions, translocations) - consult pathologist.

Reference

Rooney DE ed. Human Cytogenetics, Constitutional Analysis, a Practical Approach. 3rd ed. Oxford University Press 2001. 

Gardner RJM and Sutherland GR. Chromosome Abnormalities and Genetic Counselling. 3rd ed. Oxford University Press 2004.