CVS consists of taking some fragments of placenta (the organ that connects the circulation of the mother with her unborn baby) – the so-called chorionic villi – which are then tested to detect any genetic defects of the fetus.

Chorionic villus sampling / chorionic villus sampling

Chorionic Villus Sampling (CVS), or chorionic villus biopsy, is a prenatal invasive test that consists of taking a tissue sample from the placenta to check for chromosomal abnormalities and some other genetic problems.

The chorionic villi

At the beginning of pregnancy, a part of the embryo that forms the placenta begins to form digitiform protuberances called “chorionic villi”.

These villi are rich in capillaries: they absorb oxygen and nourishment from the mother’s blood, and give the mother carbon dioxide and other waste substances of the fetus.

Chorionic villi are formed by the progressive division of the fertilized egg, which means that they have exactly the same DNA as the embryo, including any possible genetic abnormality.

From this derives the fact that any defects present in the chorionic villi will also be present in the fetus.

Chorionic villus sampling

Chorionic villus sampling is usually done in those pregnancies in which there is a high risk that the future baby may have a serious hereditary disease.

This increased risk could be related to the fact that the woman,

  • has had a previous pregnancy with fetal problems, such as a baby born with a chromosomal abnormality or a particular mental health condition,
  • have a family history in which certain conditions such as cystic fibrosis or muscular dystrophies are present,
  • is over 35 years old.

Or that a prenatal screening test has revealed the existence of some possible problem, such as sickle cell anemia (an inherited blood disorder).

CVS is usually performed between the 11th and 12th week of pregnancy. In special circumstances it could be done even later. However, it should never be done before ten weeks.

And this is because if it is performed before the 10th week of pregnancy the risk that the collection of chorionic villus samples can cause complications, such as a miscarriage or birth defects in the baby, is greater.

Cholionic villus sampling or amniocentesis

CVS is an alternative to another examination that is done during pregnancy – amniocentesis – which is an examination aimed at detecting the existence in the fetus of specific abnormalities implemented by taking a sample of the mother’s amniotic fluid.

  • CVS can be done before amniocentesis, between the 10th and 12th week of pregnancy,
  • Amniocentesis, on the other hand, is usually done between the 15th and 20th week of pregnancy.
  • Apart from that, it may take two to three weeks for the results of amniocentesis. This means that before you can evaluate all the results, the pregnancy may already be at an advanced stage, at about 20 weeks or more.

If you are at risk of transmitting some genetic disease to your baby, your doctor or midwife can talk to you about these tests, and explain why they might be useful to you.

But also help you and your partner make a decision. They may also refer you to a genetic counselor (a healthcare professional who specializes in genetics). This will inform you about the risks of transmitting genetic diseases to your child, and will be able to give you advice on what you can do when you get the results of the tests.

How chorionic villus sampling is done

We said that chorionic villus sampling (CVS) is done by taking a sample of cells called chorionic villus cells from the woman’s placenta. This sampling can take place transabdominally or transcervically.

Transabdominal chorionic villus sampling,

  • is monitored in real time on a screen,
  • the operation takes place under local anesthesia,
  • a needle is inserted through the abdomen;
  • The needle does not enter the amniotic sac and does not approach the baby.

Transcervical chorionic villus sampling,

  • This procedure is also monitored in real time on a screen;
  • Through the cervix (the cervix) a tube is inserted to take samples.
  • Since the transcervical has a higher abortion risk than the transdominal, it is not a widely used procedure .

The test lasts about five minutes, although the entire visit takes about 30 minutes.

Patients describe chorionic villus sampling as discomfort rather than pain. However, it is also possible that cramps similar to menstrual cramps may occur.

Risks of the chorionic villus sampling test

The risk of an abortion resulting from chorionic villus sampling is less than 1%: therefore less than one pregnancy in 100.

To this specific risk, it should be added to the “underlying risk” of an abortion for natural causes that all women have at the beginning of pregnancy.

It is therefore also important to discuss any possible risk of miscarriage with your doctor/obstetrician or gynecologist.

The specific risk of abortion linked to the chorionic villus sampling test depends on the experience of the doctor who takes the sample, and on the difficulty he has in taking the sample of chorionic villi to be examined.

It is therefore important that this procedure is performed only by an experienced doctor, and that it is scheduled only after the eleventh week of pregnancy.

Vaginal bleeding may occur after the chorionic sampling. However, it is good to inquire first with your doctor so that you know in detail what you can expect after the exam and what symptoms you should pay attention to.

CVS results

Once the sample is taken, the chorionic villus sample is taken to a laboratory so that the cells can be examined under a microscope.

The number of chromosomes present in the cells will be checked, and the structure of the chromosomes will be examined to highlight the existence of any abnormalities.

If CVS is performed in relation to a specific genetic disorder, the cells in the sample will be tested for this precise disease.

The accuracy of a CVS is estimated to be around 99%. However, it is not possible to test every possible birth defect: for this reason, the results may not always be completely conclusive.

If so, additional tests may need to be done, such as looking at the chromosomes in the cells from the parents.

It may also be necessary to do amniocentesis as well: a test (which as we have said is alternative / supplementary) in which a sample of amniotic fluid is taken from the mother in order to confirm a diagnosis.

  • The first result should be available within a few days, and this will tell you if a major chromosomal problem has been discovered.
  • Full results, including those for smaller and rarer diseases, can take two to three weeks to test.
  • If the test is for a specific disorder, the results can take up to a month.

For most women who have CVS, the results will be “normal” results. This means that the child will not have any of the ailments this test was done for.

However, occasionally it is also possible to have a normal result, even if the baby is later born with either a disease that has been tested for, or another genetic condition: this is because a negative test result cannot rule out every possible genetic disorder.

If, on the other hand, the test turns out to be “positive”, the child will certainly have the disorder for which it was tested. Should this eventuality arise, the implications will need to be carefully discussed. There is no cure for most chromosomal conditions, so you need to carefully consider all options.

Options that can be

  1. to continue the pregnancy, gathering information about the disease in order to be ready to take care of the baby
  2. to terminate the pregnancy.

If you are considering carrying your pregnancy to term, talk to your doctor: he can give you important information and advice.

The possible options will depend – at the time of decision – on the number of weeks you are pregnant.

If you decide to carry your pregnancy to term anyway, you may want to talk to a counselor as well, and your doctor or midwife can help you follow this path.

Katherine Johnson, M.D., is a board-certified obstetrician-gynecologist with clinical expertise in general obstetrics and gynecology, family planning, women’s health, and gynecology.

She is affiliated with the Obstetrics and Gynecology division at an undisclosed healthcare institution and the online platform,

Leave a Reply

Your email address will not be published. Required fields are marked *