Prenatal diagnostic testing is used to find out if a pregnancy has a particular inherited or genetic condition.
Diagnostic testing is different to prenatal screening tests. Screening tests during pregnancy will give an estimate of the chance that a pregnancy has a condition. Diagnostic testing will give a definite yes or no answer.
To perform diagnostic testing, a sample of the placenta or the amniotic fluid is needed. These samples are collected via invasive procedures called chorionic villus sampling (CVS) or amniocentesis (amnio). These procedures are associated with a small risk of miscarriage. Therefore, diagnostic testing is usually only offered when there is a clinical need.
Diagnostic testing may be offered when:
- a woman receives a high chance result from a screening test (eg. non-invasive prenatal testing or combined first trimester screening)
- there are abnormal findings on an ultrasound
- there is a family history of a genetic condition
- the parents are both carriers of the same recessive genetic condition (eg. cystic fibrosis)
Information for health professionals ordering diagnostic testing.
Prenatal diagnostic procedures
Diagnostic testing is done on samples of placenta or amniotic fluid, collected via two different invasive procedures:
- Chorionic villus sampling (CVS)– performed between 11-13 weeks
- Amniocentesis – performed after 15 weeks
Diagnostic laboratory testing
There are a few different tests that can be done on the samples of placenta or amniotic fluid.
- FISH – looks to see if the cells have the correct number of chromosomes (for chromosomes X, Y, 21, 18 and 13)
- Chromosome microarray (CMA) – this test can identify extra or missing DNA in the chromosomes
- Single gene – looks to see if there is a genetic change in a particular gene that can cause a specific condition
Diagnostic procedures and testing of CVS or amniotic fluid samples is arranged through your doctor.
Depending on the test, results take between 8 and 14 days. There is usually an out of pocket cost for diagnostic testing.
Why have I been offered diagnostic testing?
Prenatal diagnostic testing is usually offered after a high chance screening test result; because of an unusual ultrasound finding or because there is a family history of a genetic condition.
Can diagnostic testing give a false result?
It is very rare for a diagnostic test to give a false result.
For testing on CVS, in some rare cases the cells in the placenta can be genetically different to the cells in the developing baby. This is known as confined placental mosaicism (CPM) and CPM can lead to a false result. Some results obtained on a CVS may require further investigation using amniocentesis.
How and when will I get my results?
The preliminary FISH test performed on CVS or amniocentesis provides results in 24-48 hours. The follow up chromosome microarray and/or conventional karyotype can take 10-14 days.
How much does diagnostic testing cost?
The cost for CVS and amniocentesis can vary depending on provider, whether you are a public or private patient and whether or not you are considered to be at a greater chance of having an affected pregnancy. There is a Medicare rebate available to partially cover the cost.
For the laboratory testing, the FISH test costs $175 and there is no Medicare rebate. The chromosome microarray and conventional karyotype are only partially covered by Medicare, so there will be some additional out of pocket costs.
I’ve received an invoice from VCGS – how do I pay?
After testing is complete, patients will receive an invoice. This can be paid by using BPAY or credit card, or by mail using a money order or cheque. Payment methods are detailed on the invoice.
To claim the Medicare rebate, take your receipt of payment to a Medicare office or online. Once processed, Medicare will send your rebate.
If you wish to speak with someone about your invoice: Free Call: 1300 557 779.