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The benefits of testing

Tom Everett, senior registrar in fetal medicine and a Clinical Lecturer at UCL, explains what NIPT is and what's novel about it.
So, I think NIPT, which is non-invasive prenatal testing and NIPD, which is non-invasive prenatal diagnosis are probably one of the most exciting developments in fetal medicine over the past, well, now about 20 years nearly since it was first developed in the late 90’s. It involves the analysis of cell-free fetal DNA. So DNA from the fetus or in fact from the placenta that is found in the maternal circulation. This new technology has various advantages over the current system. The first is that it has a higher sensitivity and specificity than the current system. And as such we are going to be able to more accurately identify those fetuses at risk of the common aneuploidies in women who wish to have aneuploidy screening.
This has the advantage of reducing the number of women who need invasive procedures and that in turn will reduce the number of miscarriages of fetuses with a normal chromosomal complement. There are two different elements to non-invasive prenatal testing. There is the screening side and then there is the diagnostic side.
So from the point of view of looking for the common trisomies: 21, 13 and 18 I can foresee this becoming a routine test. That will be offered routinely to women in the first trimester. However, it must be appreciated that what is being measured in the maternal circulation though it is called ‘fetal DNA’ it is actually DNA from the trophoblast, the placental tissue. And in about 1 in 200 occasions there can be what is called placental mosaicism so, cells with an abnormal chromosomal complement within the placental tissue whereas the fetus itself may have a normal chromosomal complement.
And this is particularly the case in and has been seen in cases of false positive testing for trisomy 18 and 13 and the sex aneuploidies of which case placental mosaicism is more common and particularly in the context of a normal first trimester ultrasound appearance of the fetus and this goes with trisomy 21 as well, because of the limitations of the placental tissue being tested. Then invasive testing is still recommended as a confirmation of this screening result.
It is separate from non-invasive prenatal diagnosis for conditions such as Achondroplasia and it is also being developed for conditions such as Cystic Fibrosis and some of the Haemoglobinopathies the thalassemias and Sickle Cell Disease in which there is a genetic mutation which is separate from the maternal or paternal genetic mutations and therefore, a diagnosis can be made. I think the social implications of non-invasive prenatal testing certainly need to be considered. Particularly as it expands from the common aneuploidies into more genetic mutations and quite possibly full fetal genome sequencing. And I think this must be carefully considered. On the face of it is not a compulsory test.
It is an optional test to the women and we are giving them a screening test that is more accurate and we are reducing the risk of miscarriage to normal fetuses. There is obviously a stressful time for the women and certainly we still see in clinical practice women who would want invasive testing because that at the moment gives a quicker result and we can do a QF-PCR in 24 to 72 hours, whereas at present the non-invasive testing takes about 10 days to come back. So, there is obviously a considerable anxiety when you get a high-risk result and some women wish to know the answer quicker.
There maybe a feeling that women are pressurised into screening but certainly the women who take screening at the moment in the UK, the combined screening, it is nowhere near 100% of women and there are a lot of women who do not opt for screening. And I think these women should not feel pressurised into being screened and that they should be counselled appropriately about the screening, about the risks and the benefits.
And then I think it is very important that if the woman does then have a high-risk result then they are then counselled appropriately about what the potential outcomes are for this baby and then this should be done in a non-judgemental way through people who are aware of the underlying disorders and complications and certainly in the UK, there are various independent charities that women can discuss their options with.

Tom Everett, a sub-speciality registrar in fetal medicine at UCLH and a Clinical Lecturer at UCL. In this segment, he explains what NIPT is and what’s novel about it. He also gives what his views on the future of NIPT and prenatal testing in general.

For your discussion: Tom Everett mentions that some might feel pressured to get tested? Do you share this worry?

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