Amniocentesis or villocentesis?

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Catherine Le Nevez
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Amniocentesis or Villocentesis

Among the tests to be performed during pregnancy most commonly recommended and known by mothers there are certainly amniocentesis and CVS. Let's try to make a sort of comparison between the two methods together to understand when they are used, what are the pros and what are the cons of each of the two.

What are they for

This is a fundamental concept to start from. I'm prenatal exams which are carried out in early period of pregnancy and that they can analyze some parameters to understand if the embryo / fetus that is growing in the maternal womb has any genetic abnormalities. Genetic anomalies are real errors in the DNA that can lead to quite serious diseases and syndromes, and in some cases even to abortion or perinatal death of the baby.

Read also: The villocentesis, when it is done and what it is used for

Main differences between CVS and amniocentesis

Since the purpose is the same, let's see which ones are main differences between the two techniques. First of all, the macroscopic difference between the two methods is the type of genetic material they are going to analyze.

  • The villocentesis picks up the tissue of the chorionic villi, that is that part of fetal tissue that is anchoring to the uterus to then develop the placenta. This is therefore a very early picking in pregnancy in the first few weeks.
  • The amniocentesis is instead the removal of amniotic fluid inside which there are fetal cells that can be analyzed. In this case, the timing is a little different and we are already in the second trimester of pregnancy, or at the end of the first if it is done very early. So as we have understood, in addition to the difference in the material analyzed, there is also a difference in timing.
  • The CVS will be performed between 9 and 13 gestational weeks (therefore in the third month of pregnancy) while amniocentesis is typically performed between the 15th and the 18th week (therefore at the end of the 4th - beginning of the 5th month) except for some cases in which it can be done earlier. I want to underline the fact that they are not different in method: both are based on the passage through the abdominal wall of the mother, both presuppose a sort of needle that picks up the different type of material, and in both cases the fetus is not touched.

Villocent or amniocentesis, selection criteria

There are general indications on the choice of one and the other exam, although lately a lot it depends on the choice of the mother (and therefore from the perception that one has of the exam) and / or of the doctor's school of thought for which one or the other method is better. Indicatively we can say that the CVS is indicated in women over 35 years of age, whether or not they have had children previously affected by chromosomal diseases of any kind. And that they have a family history in which there are genetic anomalies. Finally, even a suspicion detected by ultrasound is an indication for the execution of the CVS.

The amniocentesis it is instead indicated in women over the age of 35, and with a family history with chromosomal abnormalities, and screening tests (nuchal translucency, determination of fetal DNA on maternal blood) dubious or high-risk. So we can say that amniocentesis is recommended as in-depth study of less invasive biochemical tests that have had dubious results.

Read also: Amniocentesis, what it is and when it is done

Villocentesis or amniocentesis, cost differences

According to the new regulations as regards the services performed with the national health service, will no longer be free for women with the only risk factor over the age of 35. That is, if a woman is over 35 years old, but has no other risk factors, such as familiarity and has not done a non-invasive first level test (such as bi-test, nuchal transulcence, fetal blood determination on maternal blood, etc., etc.) will have to pay the ticket for the region of origin. On average we can say that if these tests are performed in a hospital facility the cost of the ticket is between 26 and 90 euros depending on the region of residence. Privately, however, these exams can cost approximately between 150 and 300 euros. Therefore, in reality, differences in costs between the two methods do not exist, the discriminating factor on costs or gratuitousness is given by the risk detected by the non-invasive test. If the risk is high, both methods can be free, if the risk is low, the ticket will be paid regardless of whether you choose amniocentesis or CVS.

Advantages of CVS

The main advantage of performing CVS is that it is a very early sample, which therefore makes it possible to identify very early genetic anomalies, even important ones. Let's take some examples, let's talk about trisomies (presence of an extra chromosome, such as Down's Syndrome) and let's talk about deletions or the missing pieces of chromosome. Being a very early test it allows you to evaluate alternatives early. It has a very high almost absolute reliability, even if there are cases of suspicion for which an in-depth study is then required with amniocentesis at a later time.

Disadvantages of CVS

Assuming that the method is essentially safe and that the risk of miscarriage, the main source of anxiety and concern in choosing the exam to perform, is around 1% (like any invasive exam in pregnancy and comparable to the risk of amiocentesis), I can say that the disadvantages are not relevant. In fact, if you read the statistics of the studies that compare the disadvantages and advantages of the two methods, you will find a higher risk of abortion in CVS than in amniocentesis, with a very important specification. The greater risk derives from the fact that CVS is performed in the first trimester of pregnancy and therefore there is a greater risk of miscarriage regardless of whether or not one undergoes an invasive test such as CVS.

Another disadvantage, as I mentioned before, is that some cases may be suspicious and therefore it may be necessary to repeat the exam or go to the amniocentesis as a subsequent study. This can happen in the presence of aparticular genetic anomaly and not very frequent said mosaicism (presence of two different types of DNA) or due to the fact that not only fetal tissues were taken during the sampling, but also maternal placental tissues.

The pros of amniocentesis

Surely amniocentesis is the most proven method over time, so all gynecologists know how to perform it correctly. And also less subject than the CVS to the risk of abortion (as I said before, however, this is due to the timing in which the examination is carried out) and loss of amniotic fluid.

The cons of amniocentesis

  • Not infrequently the woman who performs the amniocentesis after the examination reports having some uterine contractions minor but still present and / or vaginal blood loss, even these however of little importance.
  • More rarely, amniotic fluid may leak from the small hole in the needle with which the examination is carried out. However, this rarely causes long-term problems such as lack of amniotic fluid at term of pregnancy.
  • Finally in women with blood group with negative rH it may very rarely happen that what is called takes place isoimmunizzazione. That is, if the baby is of a positive group and the mother is negative, a reaction occurs that creates antibodies against the baby's blood group. However, this condition can be prevented by administering medication before performing the exam.

For both exams a rest of at least 12 hours is prescribed and home monitoring of the presence or absence of very important blood loss. There is no need for immobility in bed, no special attention, just a quiet life the day after the exam.

Villocentesis or amniocentesis, forum

Many questions appear on the forum to get advice on the method to choose and even if it is appropriate or not to perform these exams. The main questions concern the safety of the exam, the place of execution and the costs to be incurred. Many of you have clear and precise information about one or the other method and from the personal experiences you report we can understand how by now these methods are absolutely safe, not 100% but certainly around 99. As for the choice of one over the other, a lot depends on your personal condition and on the gynecologist who follows you.

Both are safe, but I always recommend (also for a matter of costs) to perform a non-invasive test first and only in the actual presence of risk factors go to amniocentesis or CVS depending on the gestational period you are in. As for the place, I always recommend a hospital or a large center where there are specialists in these procedures. Quantity is not always synonymous with quality so inquire about the experience of those who perform them, the presence of a dedicated clinic and the possibility of being able to have an interview to discuss the results of the exam. If you can talk to gynecologists, you can be sure that they have been paying attention to you and you are not just one of the many tests they perform every day.

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