Choose prenatal diagnosis: screening test, fetal DNA test or amniocentesis / villocentesis

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Choose prenatal diagnosis tests

In recent years, or even months, the offer of prenatal surveys has been enriching more and more, even if the general categories into which the available tests fall are only two:

  1. non-invasive diagnosis
  2. invasive diagnosis
Non-invasive diagnosis - in particular duo-test and fetal DNA test - and invasive diagnosis - CVS and amniocentesis, with classic karyotype analysis or with more innovative investigations such as microarrays or the so-called superamniocentesis.

Non-invasive tests vs invasive tests

The first thing to know is that, although more and more accurate, non-invasive tests only give an estimate of the risk of some chromosomal abnormalities, and in particular trisomy 21 (Down syndrome), trisomy 13 or 18 and possibly anomalies of the sex chromosomes. For this they are considered screening tests, not diagnostic.

In reverse, invasive tests allow a certain diagnosis, but also carry a risk of miscarriage: small, but possible. Based on very dated studies, the risk is traditionally estimated at around 1% -2% for amniocentesis and CVS respectively, but according to sector operators today it is probably lower, especially for amniocentesis: one abortion every 300- 500 surveys or even one in a thousand, according to an English publication.

Therefore, on the one hand, tests that are safe for the fetus, but which only give estimates, and on the other hand, risk tests that allow a certain diagnosis. How to choose serenely which one to do? And, even earlier, whether to require prenatal diagnosis or not? Here are the tips of Faustina Lalatta, head of the Medical Genetics Unit at the Clinic of the Polyclinic of our city.

1. Think about it first

It may seem strange, but the best way to get prepared for this is to think about it in time, if possible even before you discover that you are pregnant. This way, you'll have plenty of time to search for the information you need and to think about the topic in a calm way and not in the midst of the emotional storm that characterizes the first weeks of pregnancy.

2. Ask yourself exactly what you want to know about your upcoming baby

You can start from two assumptions:

  • Under normal conditions, the risk of having a sick baby at birth is 3-4%. In 1% of cases they are chromosomal anomalies (the main ones are 21, 13 and 18, which account for 50-70% of the total anomalies), while in the remaining cases they are malformations, such as heart disease, malformations of the kidneys or skeleton.
  • All the prenatal investigations available - ultrasound scans, non-invasive tests and invasive tests - allow us to see many, but not all, of these conditions. Faced with this situation, there are those who automatically choose the exam that still gives more certainties (amniocentesis or CVS) and those who choose to do nothing, precisely because in any case all possible risks cannot be excluded.

"Wondering what you want to know is essential for orientation" explains Lalatta. "For example: if the concern is Down syndrome, one can orientate oneself on a screening test or on an invasive diagnosis, based on the risks one intends to run, in one direction or another. if the only concern is autism, it becomes useless to think about prenatal diagnostic tests, because for the moment they cannot tell us anything about this condition ".

3. Get clear on the very concept of prenatal diagnosis

Antenatal diagnosis is not meant to confirm that the baby is okay, but to see if there are any problems. "It may seem like a subtle difference, but it's actually a major shift in perspective," explains Lalatta. "In the first case, we often approach the exam lightly, convinced that everything will be fine, and a positive (ie pathological) result is an unexpected 'blow'. In the second, however, we face it having already thought about what it will happen later, if the exam goes wrong. "

4. Immediately ask yourself what you would do if the exam revealed that the child has problems (or a high risk of having problems)

It is useless to go around the question: in the vast majority of cases, prenatal diagnosis makes sense because it provides elements for making decisions about the fate of pregnancy. It is done because, in the event that some fetal condition emerges that is considered unacceptable for the parents, they can choose to terminate the pregnancy, obviously within the terms of the law.

If you know from the start that whatever happens you will never terminate the pregnancy, it is probably useless for you to perform a screening test (which could only create unnecessary anxiety) and it is certainly useless to make an invasive diagnosis.

5. Find out as much as possible about the conditions that frighten you the most, to understand if your fears are actually justified

Perhaps, after extensive research, you can decide that that condition leads to a quality of life that seems acceptable to you, and then it may be useless to go looking for it in the uterus. Or, vice versa, you realize that the quality of life would be really unacceptable and it becomes essential to know if the fetus is affected or not, in order to eventually decide to terminate the pregnancy.

6. Ask yourself what degree of certainty you want to have with respect to the information you are looking for, because there are various aspects on the scale

  • If in the first place you just need a risk estimate of the main chromosomal anomalies, on the basis of which to decide whether or not to continue with the investigation, then you can perform the duo-test (the National Health Service passes it, upon payment of a ticket).
  • If you want some more certainty but without taking risks, then you can prefer the fetal DNA test, which today is extraordinarily accurate, especially with regard to Down syndrome: in fact, there are fewer and fewer false positives and false negatives. However, consider that the test has not passed by the National Health Service and is quite expensive: from a few hundred euros to 1000 euros and more.
  • If you want one certain diagnosis, the only way is that of invasive investigations: villocentesis (which, however, can give a doubtful outcome, in about one case out of 50) and amniocentesis.

Villocentesis, how chorionic villus sampling works PHOTO

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Villocentesis, or chorionic villus sampling, is an invasive procedure that allows you to collect fragments of chorionic tissue, a component of the placenta, which can be ...

7. If you decide on an invasive investigation, stop and think about the risk of abortion

Whether a fetal loss occurs once in every 100 exams or once in every 1000, the reality is that it does happen sometimes: the exam is done, maybe the baby is healthy, but the pregnancy is interrupted. "It is a terrible condition, for which the woman feels heavily guilty and which can have important psychological repercussions," says Lalatta. "This is why it is important to be convinced of the decision to make an invasive prenatal diagnosis".

"It may seem brutal, but you have to imagine living that situation and wondering whether losing a healthy child or having a sick child is considered worse. Only if the choice is really weighted and solid, in fact, if things go wrong it will be less difficult to come to terms with it. "Of course, it is a choice that varies a lot from woman to woman, from situation to situation, even from pregnancy to pregnancy of a same woman.

8. If you are over 35, consider that today age is no longer a sufficient factor to go directly to the invasive diagnosis

It worked like this until a few years ago, so much so that in Del Paese amniocentesis is free for women over 35. "Today, however, the existence of screening tests allows us to take an intermediate step" underlines Lalatta. If your concern is age, you can take a screening test to assess what your actual risk is, and only on the basis of this information to decide whether or not to continue with CVS or amniocentesis.

In other words, amniocentesis or villocentesis are not done just because friends have taken them or because they are 37 or 38 years old. They are done because we have thought very carefully about what we want to know, and we have decided to take the risks that these techniques entail.

9. Obtain accurate information from your doctor

"For a start, try to understand his general position with respect to prenatal diagnostic tests. It may happen that some doctors do not provide accurate information on this, perhaps because they are objectors," says the geneticist.

Information on prenatal diagnosis should be provided during the first pregnancy visit: "The doctor should try to understand what the woman expects from these tests, but above all he should explain as precisely as possible what the options are on the table: what kind of answers they give, what they entail and what are the associated risks ", Lalatta specifies. Such an explanation is unlikely to take less than 20 minutes.

10. Talk thoroughly with your partner

Before making a decision, compare your views and feelings. Being in tune or at least knowing each other's positions well is of great help in case things don't go the way you hoped.

  • prenatal diagnosis
  • test at screening
  • amniocentesis
  • villocentesis
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