Non-Invasive Prenatal Testing (NIPT)
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- What is NIPT?
- What Does NIPT Screen for?
- Who Should Do the NIPT Test?
- When is NIPT Normally Done?
- How is the NIPT Test Different From the Combined/ Quadruple Test?
- How Does the Non-Invasive Prenatal Test Work?
- Risks Associated With Prenatal Cell-free DNA Screening
- What About the Accuracy of the NIPT Test?
- What About the Results of NIPT?
When you visit your doctor during the initial days of your pregnancy, you will be given a list of prenatal tests that have to be done at different stages. These tests give doctors the essential information about your health and that of your unborn baby. This can help detect any issues like genetic disorders and birth defects to help you plan healthcare requirements if any. Blood and urine tests, as well as ultrasounds, are most commonly suggested.
What is NIPT?
Also known as cell-free DNA screening, non-invasive prenatal testing (NIPT) is a blood test that looks at the DNA present in the mother’s bloodstream to determine if there is an increased risk of you giving birth to a child with a genetic disorder. The advantage of NIPT over other tests is that it can be done early during pregnancy and is accurate compared to other screening tests. It is also more sensitive and specific than quite a few other first and second trimester screenings.
What Does NIPT Screen for?
NIPT is helpful in detecting Down’s Syndrome, Edward’s Syndrome, and Patau Syndrome, also known as Trisomy 21, Trisomy 18, and Trisomy 13, respectively. It can also pinpoint the baby’s gender and Rh blood type.
Who Should Do the NIPT Test?
Earlier, it was recommended only for pregnant women who were at high risk of giving birth to children with chromosomal abnormalities. This includes women aged 35 or older, those with an older child having genetic disorders, and women with a family history of genetic problems. It is also suggested that those who are carriers of X-linked recessive disorders like haemophilia or Duchenne’s muscular dystrophy be tested. Also, if you have an Rh-negative blood type, this test can determine if the baby has the same Rh factor or not. If not, steps need to be taken to ensure smooth delivery in some cases. Nowadays, the decision to test is to be taken by you and your doctor.
When is NIPT Normally Done?
This test is done when you are ten weeks pregnant or later and the results are known in about two weeks. It is not recommended for cases where foetal anomalies can be spotted on an ultrasound or for genetic anomalies that will not be detected by NIPT.
How is the NIPT Test Different From the Combined/ Quadruple Test?
In both these tests, a sample of maternal blood is taken for analysis. While NIPT looks at the cell-free DNA in the mother’s blood, the combined and quadruple test check’s the mother’s hormone levels. Given its accuracy rates, NIPT is considered a better tool for evaluating the chances of the baby having Down’s syndrome than the other two.
How Does the Non-Invasive Prenatal Test Work?
The NIPT takes into account the fact that chromosomes come in pairs but those with Down Syndrome will have an extra copy of the chromosome 21. In Edward Syndrome, it is an extra copy of chromosome 18 while those with Patau Syndrome will have an extra copy of chromosome 13.
Risks Associated With Prenatal Cell-free DNA Screening
There are no risks involved with prenatal cell-free DNA screenings. Getting this test done can help you avoid a few other invasive tests that can put your pregnancy at risks such as amniocentesis and chorionic villus sampling (CVS).
What About the Accuracy of the NIPT Test?
This test can predict with 97% to 99% accuracy whether your child is at risk of three of the most common genetic conditions. The reasons behind the inaccuracy of both positive and negative results are as follows:
Causes of False Positives:
This might happen due to ‘vanishing twin syndrome’, and a scan can help determine if this is the case. A false positive might also be due to some problem present in the mother rather than the baby or caused by the presence of an abnormal cell line in the placenta but not in the baby.
Causes of False Negatives:
If the amount of foetal DNA present in the sample is too little, it can result in a false negative. Technical issues can also give a false negative.
Also, when the mother is carrying twins or multiples, the result of NIPT may not be clear cut because it can be difficult to know which of the foetuses is affected without an individual amniocentesis for each.
What About the Results of NIPT?
The terms used when reporting the results will vary depending on the lab that does the testing. But usually, the results of a non-invasive prenatal screening are likely to be positive, negative, or inconclusive. Here’s what each means:
Some type of abnormality is present, and you might need to get further invasive testing done. That might mean amniocentesis or CVS.
Highly unlikely that there is any kind of chromosomal or genetic issue.
Only about 4 % of all NIPT tests turn out to be inconclusive. This might happen when there is a low amount of foetal DNA present in the sample. The NIPT might have to be repeated.
If the tests show that the baby is Rh-negative, there is no need to do anything. But if the baby turns out to be Rh-positive, your pregnancy will have to be monitored carefully depending on your health and other factors. Based on the results of your NIPT as well as results of any first trimester ultrasounds or nuchal translucency screening, your doctor might recommend further testing.
It is natural to feel anxious and concerned about the NIPT and its results, especially if it turns out that your baby might have some kind of chromosomal condition. Chromosomal abnormalities cannot be remedied or treated. Talking to your doctor and a genetic counsellor might help you get answers and decide on the future course of action to adopt.