25 July 2018

Non-invasive prenatal tests – What are they and who can benefit?

By the Editorial Comitee IVI Blog


Non-invasive prenatal tests represent a remarkable breakthrough in the way that prenatal genetic screening is carried out. In the past there have been several different types of prenatal genetic testing available, but these have presented certain drawbacks which could in some cases have been a discouragement to their use. This meant that previous generations of parents looking forward to the birth of their child had some difficult choices to make and some difficult issues to get to grips with. These issues around prenatal genetic testing pros and cons have long been a subject of close interest for expecting parents. In this article, we introduce non-invasive prenatal tests, look at how they differ from other types of genetic screening, and who can benefit.


What is the purpose of prenatal genetic screening?

Genetic testing to examine the DNA of a growing embryo is carried out in order to identify any genetic abnormalities, including some inherited diseases, but most importantly to identify any chromosomal abnormalities. The normal human genome is the complete set of nucleic acid sequences for humans, encoded as DNA within 23 chromosome pairs. The first 22 of these are identified by labels number 1 to 22. The last one is the chromosome pair that determines gender, with girls having two X chromosomes and boys having one X and one Y chromosome.

However, in three genetic conditions in particular, there is an extra copy of one of the chromosomes over and above these 23 pairs. This is known as a trisomy, which describes the condition where a chromosome appears three times in a cell, rather than the normal two times. In Down’s syndrome, the extra chromosome occurs on pair number 21 (trisomy 21). In Edwards’ syndrome there is an extra chromosome on pair number 18 (trisomy 18). In Patau’s syndrome the extra chromosome is present on pair number 13 (trisomy 13). In most cases, this is a chance occurrence and is not a condition which has been inherited from either or both parents.

This is why mothers-to-be can be offered screening to check whether this condition is present. It is also well known that parents-to-be over a certain age, particularly the mother, carry a higher chance of an abnormality occurring. These individuals, as well as those who may be at higher risk for other reasons, have been particularly encouraged to have one or more of the available types of genetic screening carried out. Those at higher risk can include those where hormone analysis and ultrasound scans have highlighted a risk, or those who have had a previous Down’s syndrome pregnancy.


Prenatal genetic testing pros and cons: what are the issues?

Before the advent of the techniques of non-invasive prenatal tests, the advantage of genetic testing was simply to alert prospective parents to the likelihood or fact of a genetic abnormality. The disadvantage came with the way that the tests were carried out, since, if there is an increased risk of having a baby with Down’s, Edwards’ or Patau’s syndromes, the woman can be offered amniocentesis to secure a definitive diagnosis. Amniocentesis is based on taking a small sample of the amniotic fluid that surrounds the foetus for testing. This procedure increases the risk of miscarriage, which occurs in one in 100 women (1%).

This leads to the prenatal genetic testing pros and cons equation which women and their partners have had to deal with in the past. This is the sensitive and delicate dilemma of whether to undergo these tests in order to be in possession of the full information that could be available, set against the small but significant risk of causing a miscarriage. This raises a completely different set of issues from those of, for example, preimplantation genetic screening that can be carried out as a matter of course during the IVF process. Most patients fully support and understand why this is a beneficial process, but the emotional response can be markedly different when the growing and developing foetus is a physical presence in their bodies.

With the advent of new types of genetic screening like non-invasive prenatal tests, stressful decisions like these can be a thing of the past.


How do non-invasive prenatal tests work?

These are examples of the new types of prenatal genetic testing which are the most complete non-invasive prenatal tests currently available. They can be given to any mother who wishes to rule out the presence of a chromosomal abnormality in her foetus but who also wishes to avoid the possibility of putting her pregnancy at risk. These prenatal genetic screening tests use advanced technology to compare foetal and maternal DNA in order to detect trisomies, i.e. abnormalities in chromosomes 21, 18 and 13. The non-invasive prenatal tests tests can identify 99.9% of foetuses with Down’s syndrome as well as other common chromosomal anomalies with excellent precision and a high degree of reliability.

This level of effectiveness has been made possible because extensive research and advances in technology have led to a non-invasive maternal blood test to replace the older and slightly risky methods. What happens is that during pregnancy, fragments of the foetus’s DNA are mixed into its mother’s bloodstream. The huge advances in the field of genetics have now made it possible for us to detect these fragments of foetal DNA in the mother’s blood for the first time and to analyse them in order to access genetic information regarding the baby’s chromosomes.

Clearly this is a development that entirely removes any risk of accidentally causing a miscarriage, since a test of the mother’s blood provides all the information we need. At the same time it helps parents-to-be to be fully in possession of all the facts they need about the genetic health of their baby without having to face any of the fears and worries associated with that small amount of risk.


Non-invasive prenatal tests: who is it suitable for and who can benefit?

A non-invasive prenatal test is recommended for all women who want the reassurance of ruling out the presence of chromosomal abnormalities in the foetus without any danger of harming the baby or putting their pregnancy at risk. It is especially suitable for those who have been found to have a high risk of chromosomal abnormalities following routine hormone analysis and ultrasound screening carried out during the first three months of pregnancy. It is also recommended in cases of a twin pregnancy or for women who have had a previous Down’s syndrome pregnancy.


IVI: research is in our DNA

Developments in prenatal chromosomal screening are just one example of the benefits that ongoing scientific research can bring to the work that we do. We at IVI are committed to advancing research and technology in the field of assisted reproduction and proud of our unique record. For example in 2016, four gynaecologists from IVI were ranked among the seven top researchers in reproductive biology according to the h-index, in a study identifying the scientific output with the highest impact worldwide. The study simultaneously measures the quantity and quality of work carried out by researchers, taking as a reference their publications and the number of times these have been cited by other professionals around the world.


Browse our website and find out more

Of course, not all pregnant women will feel the need for the type of reassurance that can be provided by non-invasive prenatal tests, and if that is the case in your particular circumstances, all well and good. You may still like to browse our website to check any facts or clear up any queries or uncertainties that you may have. Or take a look at our video introducing IVI and the services we offer across a whole range of preconception, prenatal and assisted reproduction techniques and services.

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If you feel that this breakthrough blood test can add to the sense of serenity and calm that you have always pictured as part of your pregnancy, go ahead and get in touch. There are no strings, and we’ll be happy to hear from you. Contact our call centre whenever you feel ready.




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