NIPT is a blood test that looks for common genetic conditions in early pregnancy. It is most often used to look for chromosomal disorders that are caused by changes in the number of chromosomes due to an extra or missing copy of a chromosome.
What is being tested?
There are DNA fragments circulating freely in our bloodstream (also known as cell-free DNA) which are released by cells during normal cell turnover. During pregnancy, a small amount of this DNA comes from the baby in the womb (the fetus), specifically from cells which make up the outer layer of the placenta. Non-invasive prenatal testing (NIPT) measures the amount of DNA from the fetus circulating in the mother’s blood stream. More specifically, it measures the quantity of fetal DNA coming from chromosome 21,13,18, X and Y. If the baby has an extra one of these chromosomes, the test is able to measure this excess amount of DNA. This way, NIPT is able to detect chromosome conditions such as Down syndrome (due to an extra copy of Chromosome 21, or trisomy 21), Patau syndrome (trisomy 13), Edward syndrome (trisomy 18) and identify the sex of the baby.
How is it used?
NIPT is used to assess the risk of a baby being affected by Down syndrome or other less common chromosomal disorders. It is requested early in pregnancy in women who are concerned about having a child affected by trisomy 13, 18 or 21. This is a screening test. Positive results need to be confirmed by an invasive diagnostic test such as amniocentesis or chorionic villus sampling which provides a definitive answer on the chromosomal makeup of fetal cells by karyotyping or microarray analysis.
When is it requested?
NIPT is available to all women during pregnancy. NIPT has been assessed as a useful screening tool in pregnancies where the following risk factors are present:
What does the result mean?
NIPT is a screening test which has better performance than other first or second trimester blood tests used for Down syndrome screening which are based on measuring the concentration of a number of biochemical markers in the mother's blood. It has a sensitivity of around 99.5 per cent for detecting Down syndrome, i.e. less than one case in 100 will be missed by the test. It also has a very high specificity. When NIPT is used in pregnancies which have a very high pre-test risk of Down syndrome (trisomy 21), false-positive results are not common (although it still possible). However, for women who are in a lower risk group such as younger women, it is known that false-positive and false-negative result rates will be higher. Also, the sensitivity and specificity of the test are not as good for rarer chromosomal disorders such as trisomy 13 and 18 and sex chromosome disorders. They are lower still for other microdeletion syndromes.
First trimester blood test and 12 week ultrasound scan are still recommended to look for other structural or chromosomal abnormalities.
Is there anything else I should know?
NIPT is currently available primarily through private laboratories. It is not covered by Medicare or private health insurance. The cost is approximately $400-500 per test.
Very infrequently the test may not give a result as there may be insufficient DNA from the baby in the mother’s blood sample. This is more likely if the test is conducted in very early pregnancy.
Common questions
Many pathology laboratories in Australia offer blood specimen collection for NIPT, but may either do the test themselves or send the sample to one of the specialist laboratories, for testing. Depending on where the testing is done the results may take 5 -14 days.
First trimester ultrasound remains an important screening tool for congenital abnormalities which may, or may not have a chromosomal cause.
NIPT can be used as a second-line screen following a combined first trimester ultrasound and blood testing (cFTS), using the following principles (as a guide only- the optimal screening pathway for each patient likely varies depending on individual clinical circumstances and should be adapted for each patient in consultation with your medical practitioner):
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