Non-invasive prenatal testing

Sonic Genetics provides non-invasive prenatal testing (or NIPT). This is a blood test that screens for common genetic conditions in the developing fetus. The conditions screened can include:

  • Down syndrome (an extra copy of chromosome 21; i.e. “trisomy 21”)
  • Edwards syndrome (an extra copy of chromosome 18; i.e. “trisomy 18”)
  • Patau syndrome (an extra copy of chromosome 13; i.e. “trisomy 13”)
  • Abnormal numbers of the sex chromosomes; i.e. of the X or Y chromosomes
  • Abnormal gain or loss of a large segment of a chromosome
  • Abnormal gain or loss of an entire chromosome in just part of the developing placenta or fetus

The test requires a single blood draw, and can be done once you have reached 10 weeks’ gestation. Collecting a maternal blood sample for NIPT poses no threat to the fetus.

During your pregnancy, your healthcare providers will offer various tests to help you assess your pregnancy. Some genetic conditions run in families. Others, such as Down syndrome, typically do not. They can happen in any pregnancy. Although the likelihood of a baby having Down syndrome increases with the mother’s age, most babies with Down syndrome are born to women under 35 years of age. As part of your care, you will be given the option to screen for chromosome conditions, which are genetic disorders that can affect the physical and mental development of a child.

There are a range of tests available to screen for chromosome conditions during pregnancy. For many years, screening for chromosome conditions was done as a test of the mother’s blood (“maternal serum screening”) and an ultrasound at approximately 12 weeks gestation. If there was an increased probability of a chromosome condition, a definitive diagnosis could be achieved by examining cells from the fetus collected by an invasive technique such as chorionic villus sampling (CVS) or amniocentesis.

Within the last few years, NIPT has become available as a much more accurate screening test for these common chromosome conditions. This has dramatically reduced the need for invasive tests such as chorionic villus sampling or amniocentesis, although these may still be required to confirm an NIPT result. 

Sonic pathology practices have provided, and continue to provide, maternal serum screening and analysis of CVS and amniocentesis samples. We are also one of the most experienced providers of NIPT in Australia.

nipt harmony test

What NIPT options are available?

Standard NIPT

The primary purpose of NIPT is to identify pregnancies in which there is an increased chance of a common trisomy i.e. Down syndrome (trisomy 21), Edwards syndrome (trisomy 18) or Patau syndrome (trisomy 13). The standard NIPT screens for just these disorders and is included on all of our NIPT reports. The accuracy of NIPT is highest for detecting these three conditions.

There are a number of options available with NIPT. If you are considering any of these options, we recommend that you discuss this with your partner and doctor. Some of the options may provide information that you would prefer not to know or that is too uncertain for it to be useful to you.

Each of these options must be requested by your doctor prior to your blood sample being collected.

 

Option: fetal sex [no charge]

There is an option to screen for fetal sex; this is free of charge. This tests for the presence of DNA from a Y chromosome (the male chromosome) in the mother’s blood.

The accuracy of NIPT for determining fetal sex is very good (99%), but it is not perfect.

 

Option: sex chromosomes [no charge]

There is an option to screen for abnormal numbers of X or Y chromosomes; this is free of charge. This option is not available in twin pregnancies.

Males usually have one X and one Y chromosome (XY), and females usually have two X chromosomes (XX). An abnormal number of sex chromosomes can cause Turner syndrome (a single X chromosome) and Klinefelter syndrome (XXY). These conditions are typically less severe than the three trisomies mentioned above. NIPT can also identify the presence of an additional Y chromosome (XYY) or X chromosome (XXX); most people with these chromosomes look and function normally and are not aware of the additional chromosome.

The accuracy of NIPT for abnormalities of sex chromosome number is very good (>90%), but not as good as for the trisomies.

 

Option: genome-wide NIPT [additional charge]

Sonic Genetics provides an option for genome-wide NIPT. This is available for an additional charge. 
Genome-wide NIPT screens for a range of other chromosome abnormalities that can occur in pregnancy:

  • The gain or loss of a segment of a chromosome (rather than the whole chromosome, as in trisomy). This covers all chromosomes except the X and Y chromosomes. The segment involved must be at least 7 million base pairs long; this about 1/6th the size of chromosome 21. Such gains or losses are usually associated with abnormalities in the growth or intellectual development of a child. Please note that the gain or loss of an even smaller chromosome segment can also cause abnormal growth or development; NIPT cannot detect such abnormalities. 
  • The gain or loss of an entire chromosome, with this abnormality being restricted to only some cells; the remaining cells have the normal number of chromosomes. Such mixtures of normal and abnormal cells are often limited to the placenta, with the fetus having normal chromosomes. However, the chromosome abnormality can interfere with the function of the placenta and may indirectly affect the fetus.

The accuracy of genome-wide NIPT for detecting these abnormalities is good, but not as good as for sex chromosome abnormalities. There is limited information about the accuracy of genome-wide NIPT in twins. 

Further details of these disorders can be found here.

Why use Sonic Genetics for NIPT?

We have been providing NIPT since 2013, and brought the test into our Australian laboratories in 2015. Since then, we have screened more than 200,000 women. We constantly review the medical literature on NIPT and the performance of different methods of NIPT to ensure that we are providing you and your doctor with a screen that meets the highest standards. Our testing is now provided in two of our Australian laboratories, both of which are accredited by the Australian regulatory authorities for this class of testing. We have numerous genetic pathologists and experienced medical scientists who supervise the delivery of this test.

The information on this website is provided for your general information and is not a substitute for the specific advice of your treating doctor.