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About Non Invasive Prenatal Tests (NIPT, sometimes called Harmony™ Test) and Nuchal Translucency (NT) Scans.

Pregnant women in the UK are currently offered screening for trisomy 21 (Down Syndrome) at the first trimester Nuchal Translucency (NT) scan on the NHS. The NT measurement is undertaken with ultrasound and this measurement may be combined with serum protein markers in the blood to give a combined risk factor. The detection rate within the NHS when a combined test is used is currently nearly 90%. If the screen is positive, then an invasive procedure is offered in the form of either amniocentesis or CVS sampling. Amniocentesis and CVS sampling are highly accurate, however, they carry a small but significant (up to 1%) risk of miscarriage.

Advances in research have enabled a new Non Invasive Prenatal Test or NIPT to provide more accurate results and higher detection rates during pregnancy. In 1997, it was reported that fetal DNA was present in the maternal blood deriving from the placenta and that it could be detected as early as the first trimester onwards. This research proved that maternal blood is a reliable source for prenatal testing and diagnosis and, since then, significant breakthroughs have been made in the identification of fetal chromosome / trisomy abnormalities. In addition, fetal blood group status and fetal sexing are also identifiable from maternal blood samples. Further research has also shown that fetuses with Down Syndrome have a higher concentration of fetal DNA within maternal blood making it a reliable method of detection.

Current research shows that a pregnant woman from 10 week’s gestation is the earliest time for blood collection. The blood test is combined with an ultrasound dating scan to establish the gestational age of the foetus before the blood sample is taken, this ensures quality control of the NIPT. It has been proven that using this method reduces the chance of a false-negative result due to insufficient fetal DNA concentration. The amount of fetal DNA in the maternal blood increases with gestational age, and if samples are taken too early within a pregnancy false negative results are more likely.
NIPT Results.

For trisomies 13 (Patau’s Syndrome), 18 (Edwards Syndrome) and 21 (Downs Syndrome) the NIPT detection rates have demonstrated a sensitivity greater than 99%. Approximately 4% of samples fail due to insufficient fetal DNA (fDNA) being present and it is recommended that a second blood sample is taken in these cases.

Within multiple pregnancies, the fDNA is approximately double that of a single pregnancy. For a di-chorionic (non identical) twin pregnancy, results may be discordant and are still in the early stages of development. According to the RCPA in 2014, NIPT has not been sufficiently evaluated in multiple pregnancies however studies are continuing. Research undertaken by the American College of Obstetricians and Gynaecologists in 2012 states that initial studies on twins demonstrate accuracy in a small cohort however further information is required before it can be recommended.

For those women who have an abnormal NIPT, invasive prenatal testing is still currently recommended to confirm the diagnosis in the form of CVS or amniocentesis.

In recent studies it was concluded that detailed prenatal counselling is required to ensure that women have an understanding of the implications of the results. This was also concluded within research undertaken by the RCOG in 2014 that stated all clinicians should have knowledge of the counselling issues involved within the test.

It is considered that in time NIPT will become the primary screening process for chromosomal abnormalities in pregnancy. Ultrasound scanning will continue to be clinically important for many reasons including its ability to detect non-chromosomal abnormalities and complications during pregnancy. In the long term, it is hoped that the use of NIPT will eventually reduce the loss of uncomplicated pregnancies due to miscarriage from an unnecessary invasive procedure.

Going for any type of screening should be considered carefully; try to imagine beforehand how you would feel if the results were positive, what you would do with this information and who you may or may not share it with. Ultrasound Direct offers both NIPT and NT services, find out more and book online by clicking on the following: