NIPT by TDL
Non Invasive Prenatal Screening ( NIPS) has been provided in the form of the NIPT by TDL (formerly Harmony) test at GCRM since 2012. NIPT by TDL led the provision of NIPS and was introduced in to Scotland by Professor Alan Cameron at GCRM.
The NIPT by TDL is an accurate way of estimating the risk of a baby having Down syndrome (Trisomy 21), Edward’s syndrome (Trisomy 18) or Patau syndrome (Trisomy 13).
The NIPT by TDL test differs from traditional screening for chromosome abnormalities, such as, the Combined Test and the Quadruple Test because it analyses the baby’s DNA rather than ultrasound features and/or hormone levels in the blood. This means the NIPT by TDL test is more accurate than these traditional tests for estimating the risk of a baby being affected by Down, Edward’s or Patau syndrome.
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What is trisomy 21, 18 or 13?
Most of us have a normal complement of chromosomes, this being 46 in total, made up of 23 pairs. In trisomy, there is an additional copy of a particular chromosome, resulting in a total of 47 chromosomes. The most frequently occurring trisomy is trisomy 21, more commonly known as Down syndrome. Other trisomies include trisomy 18 and trisomy 13, known more commonly as Edwards and Patau Syndrome, respectively.
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Trisomy 21 is found in around 1 in 700 births and the risk of having a baby affected by trisomy 21 increases with advancing maternal age. The condition is associated with learning disability and some structural problems within the baby’s major organs, most commonly heart abnormalities. The life expectancy is around 60 years.
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Trisomies 18 and 13 are found in around 1 in 7,000 births and the risk of having a baby affected by one of these trisomies also increases with advancing maternal age. These conditions are associated with severe learning disability and multiple physical abnormalities. Most affected babies die before or soon after birth, and rarely survive beyond the first year of life.
What is the NIPT by TDL Test?
DNA is the genetic material found in each and every cell in our body. The pattern of DNA makes up the genes that code for our characteristics, such as hair and eye colour, and any genetic conditions we may have or carry. Cell free DNA is genetic material which comes from the baby but can be detected in the mother’s blood during pregnancy. The exact mechanism as to how the baby’s DNA – the cell free DNA - finds its way into the maternal bloodstream is not clear. However, scientists have discovered that cell free DNA is present from early pregnancy and is undetectable 2 hours after the baby is born.
The NIPT by TDL Test analyses cell free DNA in maternal blood and gives a strong indication of whether the baby is at high or low risk of having trisomies 21, 18 and 13.
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How accurate is The NIPT by TDL test?
The NIPT by TDL test detects 99% of babies with Down and Edwards syndrome. For Patau’s syndrome it will detect 92-99% of babies, depending on the test you choose.
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Why are the results not 100% accurate?
The only way to know for sure whether or not a baby has a chromosome abnormality is to have an invasive test such Chorionic Villus Sampling (CVS) or amniocentesis. Invasive testing gives very accurate results because genetic material obtained directly from the pregnancy is used for analysis. However, as these procedures involve inserting a needle into the womb to obtain genetic material, they carry a small but significant risk of causing a miscarriage (1%).
NIPT is a screening test and therefore in rare circumstances positive and negative results can be inaccurate. The test will detect up to 99% of babies affected by Down, Edwards or Patau syndrome. A false positive result occurs in less than 0.3% of cases (1:300). This is significantly better than traditional screening tests which have a detection rate of 75-95% for a false positive rate of 3-5%.
This means that women choosing NIPT will benefit from a test that detects a greater proportion of babies affected by chromosome abnormalities, and women will be less likely to require an invasive test (which carries a 1% chance of miscarriage) following screening.
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What would the results show?
If the NIPT by TDL test shows there is a high chance that the fetus has trisomy 21, 18 or 13 it does not mean that the fetus definitely has one of these defects. If you want to be certain you should have a CVS or amniocentesis.
If the NIPT by TDL test shows that there is a low chance (less than 1 in 10,000) that the fetus has trisomy 21, 18 or 13 it is unlikely that the fetus has one of those defects.
When do I expect to get the results?
The results from the test will generally be available within 1 week and you will be notified as soon as we receive them by email if they are low risk. High risk results will be discussed over the phone.
In about 5% of cases the test does not give a result. This is due to technical problems with the analysis of the sample and does not suggest there is a problem with the baby. We will repeat the test at no cost and are able to get a result in over 50% of cases.
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The current patient information leaflet on NIPT by TDL is found here
In recent years other companies have become involved in NIPS and there is now an opportunity to provide patients with greater choice of product and price.
The other NIPS products that are currently available through Prenatal Dx are below.