When you are pregnant

Most pregnancies result in the birth of a healthy baby. However some pregnancies can have chromosome abnormalities and can result in miscarriage or the birth of an abnormal child. You may be familiar with Down syndrome which is caused by a chromosome abnormality, also referred to as Trisomy 21. There are also other chromosome abnormalities that can affect your baby.

Our prenatal diagnosis laboratory offers a non-invasive test of the mother’s blood to screen for Down syndrome pregnancies. If the screening test indicates a high-risk pregnancy, a diagnostic chromosome test can be performed to more accurately determine if your pregnancy is affected by Down syndrome. The chromosome test requires either a chorionic villus or amniotic fluid sample, which can be arranged by your consulting doctor.

We offer the following tests during pregnancy:

  

First Trimester Screening (biochemistry) test for Down syndrome

A biochemical screening test for Down syndrome has been developed that increases the likelihood of Down syndrome cases being detected in the first trimester of pregnancy. The test involves combining the results of a test of the mother’s blood and a special ultrasound screening test. This is a screening test that can pick up about 90% of babies with Down syndrome.

A maternal blood sample must be taken after 10 weeks but before 14 weeks of gestation (at the border of the first and second trimesters). Your blood can be collected by your doctor or any collection centre of Symbion Health, or, by special arrangement, at other pathology centres. If you receive a high risk result your doctor will discuss options with you for further testing.

For more information on this test, see FTS Biochemistry test for Down syndrome and Biochemistry tests.

  

Rapid chromosomal aneuploidy screening

Chromosome aneuploidy is the numerical loss or gain of chromosomes, which can be the cause of miscarriage or an abnormal child. You may be familiar with Down syndrome which is caused by gain of chromosome 21, ie Trisomy 21.

Conventional chromosome analysis requires prenatal samples (chorionic villus or amniotic fluid) to be grown or cultured, which is the reason why it can take up to 2 weeks to get a final result. Alternatively, screening of the five most commonly found chromosomes abnormalities (X, Y, 13, 18 and 21) can be performed within 1-2 working days.

This can be done using uncultured cells by FastDNATM or FastDNAplusTM. A prenatal chorionic villus or amniotic fluid sample is required for this test. Your ultrasound specialist or consulting doctor can arrange for this test to be done.

This image shows FastDNA results that tells us whether a pregnancy is affected by a problem for 5 of the most common chromosome abnormalities; chromosomes 13, 18, 21, X and Y. 

 For more information on FastDNA tests, see FastDNA.

 

Prenatal diagnostic testing

Prenatal testing is typically performed on those pregnancies identified as high risk of either a chromosomal or molecular DNA genetic disorder. Samples are typically collected by:

Chorionic villus or amniotic fluid samples are collected by an ultrasound specialist or consultant doctor. Your General Practitioner or referring doctor can arrange a referral for a prenatal sample collection. You may wish to visit Sydney ultrasound for Women at www.sufw.com.au to arrange prenatal sampling.

 

This image shows the paired chromosomes from a pregnancy of a normal male.

Unfortunately, chromosome analysis requires chorionic villus or amniotic fluid samples to be grown or cultured (see Tissue culture), which is the reason why it can take up to 2 weeks to get a final result. Not surprisingly, most parents waiting for a prenatal test result find it difficult waiting for the result of the chromosome test. So, if at any time you would like to know how your test is progressing, please do not hesitate to contact the laboratory to see how your test is progressing.

Alternatively, you might also wish to consider our rapid chromosome testing which can be performed within 1-2 working days. See our FastDNA or FastDNAplus tests. These tests are add-on tests which are to be requested at the time of your prenatal sample collection.

Prenatal molecular genetic tests can be performed for individuals who are known carriers of a previously identified and characterised genetic mutation (e.g cystic fibrosis). Please contact us to determine whether we can provide a prenatal test for you. If the genetic condition has been identified and the mutation characterised in your family previously we will most likely be able to offer you a test.

For more information, see Cytogenetics - chromosome testing or Molecular DNA testing.