Prenatal Diagnosis

Cytogenetic prenatal diagnosis studies the fetal karyotype and is performed on either chorionic villus or amniotic fluid samples. The discovery of an abnormality allows the option of termination, or a more suitable obstetric management.

The prenatal team aims to deliver an efficient and accurate service for all obstetricians.

Amniotic Fluid

Following amniocentesis the amniotic cells require culture for a number of days prior to their harvest. The final result takes at least 8 days to be completed.

We endeavour to obtain a result within 14 days. The majority are reported within the range of 8-11 days. Small samples and heavily blood-stained samples are likely to take slightly longer.

Amniotic fluids should be collected into sterile plain tubes and transported immediately to the laboratory at room temperature. A sample of 15-20 mL is desirable.

If samples are unable to be immediately dispatched to the laboratory they may be safely stored at 5° C prior to transportation.

Under no circumstances should the specimen be frozen as this will result in cell death.

Chorionic Villus Sample (CVS)

Upon arriving in the laboratory, the chorionic villus sample is carefully examined and dissected in preparation for culture.

An optimal sample size for cytogenetic analysis is 10mg. Any smaller sample may require longer time to achieve the result. For adequate samples, results can be obtained within 6 days.

Where additional tests are required (eg. specialised DNA tests), an additional 5-10 mg of tissue must be collected. We will not issue a cytogenetic result unitl all results are available.

If samples are unable to be immediately dispatched to the laboratory they may be safely stored at 5 ° C prior to transportation.

Under no circumstances should the specimen be frozen as this will result in cell death.

Limitations of the Test

Mosaicism can not be excluded. Generally 15 cells are examined from two independent cultures. This allows for 19% mosaicism or greater to be excluded with 95% confidence limits.

Cryptic subtelomere deletions/duplications and microdeletions syndromes may not be detected with current technology.

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