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What is non invasive prenatal testing (NIPT)?

Pregnancy Dr Erin Nesbitt-Hawes Director
The new NIPT has dramatically improved the accuracy of prenatal screening for the common trisomies. It typically detects 99% of pregnancies with trisomy 21, with a false positive rate of less than 0.1%.

Non Invasive prenatal testing (NIPT) is a method to look at the genetic information that your baby has.  It works on the basis that the baby sheds this cell information and this is transported around in our blood (the technical name is  cell-free DNA  or cfDNA).  This material contains both your own and your baby’s genetic information and through the test may detect major chromosomal abnormalities such as Down syndrome.   This is a ‘trisomy’ where instead of the usual 2 copies of chromosome 21, there are in fact 3.  This trisomy arrangement may also occur with other chromosomes including chromosome 18 (called Edwards syndrome) and chromosome 13 (called Patau syndrome).  The test allows for a chromosome map, including sex chromosomes to be made and to show any abnormalities.

The main advantage of this test is that it can be performed early – from 10 weeks of pregnancy and is not associated with a risk of miscarriage because it is a blood sample taken from your arm. As with many tests, there are limitations including the fact that it is considered a screening test and therefore is not 100% accurate. Sometimes the blood sample doesn’t contain enough cfDNA and a new sample will need to be collected at a later stage in the pregnancy. There are certain medical and pregnancy related conditions that mean that this test is not useful and your doctor can help give you further information regarding this issue.

If the test suggests that the baby has Down syndrome, or other type of chromosomal abnormality, it is recommended that you have an amniocentesis for confirmation. It is also important to realise that this test doesn’t check for all chromosomal abnormalities or developmental problems in your baby, it’s limited to the 3 major chromosomes (21,18 and 13) and your babies sex chromosomes.

NIPT does not check for any structural abnormalities (such as spina bifida) that may be detected at your 12 week ultrasound. NIPT should therefore not be seen as a replacement of the 12 week ultrasound scan. There is a very small risk that the NIPT may pick up a chromosomal abnormality or tumour that originates from you, and this would require further investigation.

The test is available at some maternity hospitals and private ultrasound specialists. It is an expensive test with costs ranging from $500 to $1200.  Your sample will be sent and analysed overseas, and it will take 10-14 days for the results to be returned.