NIPT

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What is NIPT for Down Syndrome?

Non-invasive Prenatal Testing (NIPT) is a prenatal screening done by collecting a mother’s blood sample to identify the risk of the fetus being born with certain chromosomal disorders. However, a screening like NIPT cannot determine whether the baby has a chromosomal disorder, only the likelihood of having that condition. But even though it can’t tell whether the baby has a genetic abnormality, it is highly accurate — 97 to 99 percent accuracy for three of the most common conditions. Down syndrome, Edward’s syndrome, Patau syndrome. The results of a NIPT screening can help determine whether to have a diagnostic test like Chorionic Villus Sampling (CVS) or amniocentesis. CVS and amniocentesis analyze a baby’s own genetic material, collected from the placenta or amniotic fluid, respectively, to tell with 100 percent certainty whether a baby has a chromosome abnormality. However, they are invasive, which means they slightly increase the chance of miscarriage.

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Frequently Asked Questions

How do NIPTs Work?

NIPT works by analysing fragments of DNA from the baby, which are naturally present in the mother’s bloodstream. These fragments are called cell-free DNA (cfDNA).

Digital analysis of this cfDNA can identify babies with the following chromosomal abnormalities:

The results are reported as a probability. A low-risk test result would be less than 1 in 1,000 likelihood (or a 0.01 per cent chance that the baby has the abnormality), while a very high-risk result would be 1 in 2 likelihood (or a 50 per cent chance the baby has the abnormality).

As it is only a screening test, if the result shows a high likelihood of a chromosomal abnormality, it’s still necessary to carry out a diagnostic test, such as CVS or amniocentesis, to determine whether the baby has the abnormality.

NIPT results are usually returned within 15 days if the samples are sent overseas for analysis.

What Will NIPT Reveal?

The results of a NIPT will indicate the likelihood – or risk factor – that the baby has one of the abnormalities tested for and does not provide a “Yes/No” answer.
If the baby is highly likely to have an abnormality, the obstetrician may suggest a diagnostic test, such as CVS or amniocentesis.
NIPTs only test for specific chromosomal abnormalities. They can’t detect major malformations such as spina bifida (defect in the baby’s spine), so the mother should still have an ultrasound at around 12 weeks to see how the baby develops.
The mother can choose to have a NIPT instead of a first trimester combined screening test, an ultrasound and a blood test. A combined screening test is not as accurate as a NIPT, which is claimed to have an accuracy rate higher than 99 percent.
Some patients choose to have a NIPT after another first-trimester screening test returns a high-risk result.

When is the NIPT Test done?

NIPT can be performed any time after 9 weeks into the pregnancy — earlier than any other prenatal screening or diagnostic test.
In comparison, nuchal translucency screening is done between weeks 11 and 13; CVS is done at 11to 13 weeks; the quad screen is completed between weeks 15and 21, and amniocentesis is usually performed between weeks 16 and 20.

How is NIPT done?

Because a NIPT involves only quick blood draw from the mother’s arm with a needle and syringe, it’s safe for the mother and the baby. The sample is then sent to a lab, where the baby’s DNA fragments in the blood is analysed for signs of abnormalities.

How is NIPT different from the combined/quadruple test?

- Although both tests involve a sample of maternal blood, NIPT analyses the cell-free DNA in the mother’s blood, whereas the combined and quadruple test analyses the mother’s hormone levels.
  With more than 98% accuracy, NIPT is more accurate than the first trimester combined test or second-trimester quadruple test for estimating the chance or the risk that the baby has Down syndrome.

Accuracy and Reliability of NIPT

The NIPT is still a highly accurate screening test that gives a risk factor, not a diagnosis.
NIPT can be used as screening tests for low-risk and high-risk women. As the chance of genetic disorders increases with age, it’s expected that older women would benefit most from testing and may be able to avoid invasive tests.
There are several reasons why false-positive results happen; for example, if the test is done early in the pregnancy, it may detect DNA leftover from a vanishing twin that has been absorbed by the mother or by the surviving twin.
In rare cases, maternal cell-free DNA may be mistaken for the baby’s, and the mother’s genetic problems may be attributed to the baby.
If the mother is overweight or obese, there may be too little baby DNA in her blood, which may cause a false-negative test result or an indeterminate result.
There is another possible reason for inaccurate NIPT results: cell-free fetal DNA comes from the placenta, and there are sometimes “cell lines” grow in the placenta but not in the baby.
This may cause a false-negative test result if an abnormal cell line is present in the baby but not present in the placenta, or a false positive if present only in the placenta, not in the baby.

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