How to choose prenatal diagnosis tests? Non-invasive screening tests such as duo-tests or fetal DNA tests, or invasive diagnostic tests such as amniocentesis and CVS?
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:
- non-invasive diagnosis
- 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% respectively for amniocentesis and CVS, 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 Mangiagalli Clinic of the Milan Polyclinic.
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 issue 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 of these conditions, but not all. 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 choose a screening test or 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, you 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, you 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 regarding the information you are looking for, because there are various aspects on the scale
- If in the first place you just need an estimate of the risk 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 from the National Health Service and is quite expensive: from a few hundred euros to 1000 euros and …