In some cases, it becomes necessary to obtain the most reliable information about the chromosome set of the fetus to determine the fate of pregnancy. Methods of prenatal assessment of the state of the embryo with penetration into its habitat are called invasive. In the first trimester, a chorionic villus sampling (CVS pregnancy test) is invasively performed to diagnose possible pathologies of the fetus.
CVS Pregnancy Test
A chorionic villus sampling is a procedure of taking a microscopic piece of a villous chorion, the future placenta, for analysis.
This piece of chorionic villi, genetically identical to the fetal genes, will allow determining the karyotype. Also, it allows characterizing the chromosome composition, as well as the genetic health of the future baby.
Purpose of CVS:
A sample of the villous chorion is used to identify deficiency and / or genetic diseases in the fetus.
What Is CVS Pregnancy Test?
- The placenta is located in the uterus and connects the fetus with the mother. Its purpose is to provide the fetus with all the energy and oxygen it needs. The placenta consists of a villous chorion. For the CVS pregnancy test, a small sample of the placenta is taken for the analysis. The obtained cells can be checked immediately – directly, or after their growth.
- The sample of the villous chorion is taken at 10-13 weeks of gestation.
- During the CVS pregnancy test doctors check the chromosomes of the fetus (karyotype). This analysis allows diagnosing Down’s syndrome (an additional 21st chromosome), as well as identifying excess or deficiency of other chromosomes. You can also identify a partial excess or lack of chromosomes. But usually this is a rare phenomenon. In some cases geneticists recommend a more accurate analysis of the chromosomes of the fetus on the molecular system (“genetic chip”).
- Diagnosis of genetic diseases. In the presence of increased risk, the analysis of embryonic cells is carried out. In this case, doctors establish the presence or absence of the disease. Technically, many analyses of embryonic and amniotic fluid cells can be performed. But in practice only relevant tests are carried out for a specific case, in accordance with the risk of having a child with a specific disease. For example, a placenta biopsy (a sample of a villous chorion) identifies the presence of a fragile X chromosome syndrome. Such an analysis is done only when it is known that the mother is the carrier of the disease.
Advantages of CVS Pregnancy Test
Doctors take the sample of the villous chorion in the first trimester of pregnancy. Therefore it is possible to get an answer if there are anomalies at an early stage. If it was found that the fetus suffers from any deficiency or disease, you can make a surgical abortion (scraping). Abortion at a later date (at 19-21 weeks) is more difficult, more prolonged, more unpleasant and more painful for a woman. Therefore, if the probability that the fetus is sick or suffering from any deficiency is 25-50%, doctors recommend taking the CVS pregnancy test. But even if the probability of this is lower than 25-50%, some women prefer to pass this analysis instead of an amniocentesis, so as not to interrupt pregnancy at a later date.
Possible Complications after the Analysis
- The probability of miscarriage after the CVS pregnancy test is 1-2%. It is twice higher than the probability of miscarriage after amniocentesis;
- The scientific literature reports cases of possible defects of the hands and feet in the fetus due to a sample of the villous chorion. But it is possible only if you make the analysis too early, before the tenth week of pregnancy;
- Sometimes the results are unclear. It is impossible to understand whether the fetus suffers from a disease or it is a technical malfunction. In this case, doctors suggest additional tests, such as amniocentesis or taking a blood sample of the fetus.
Should a Woman Do the CVS Pregnancy Test?
A chorionic villus sampling helps future parents know whether the baby has chromosomal disorders. For example, Down’s Syndrome, Edwards Syndrome, and genetic diseases such as cystic fibrosis.
This test is useful for pregnant women who, according to the results of screening of the first trimester, have an increased risk of having a child with chromosomal or genetic abnormalities.
What Diseases Can a CVS Pregnancy Test Reveal?
- Down’s Syndrome
- Trisomy 13 and trisomy 18 (Edwards syndrome)
- Turner syndrome
- Klinefelter’s syndrome
- Cystic Fibrosis
- Sickle cell anemia, etc.
CVS pregnancy test can detect about 100 rare chromosomal and genetic syndromes.
What Is the Difference Between the CVS Pregnancy Test and Amniocentesis?
The main advantage of chorionic villus sampling is that it can be done much earlier: already at 10-13 weeks of pregnancy. Amniocentesis is performed no earlier than 16 weeks of pregnancy.
The results of chorionic villus sampling come earlier. Within the first week you will be able to learn the results of the examination. At the same time, the results of amniocentesis are available 2-3 weeks after the procedure of amniotic fluid intake.
And yet, the risk of miscarriage after a CVS test is higher than after the amniocentesis. Unlike amniocentesis, a chorionic villus biopsy cannot detect such serious anomalies in the development of the child’s nervous system as spina bifida. In order to find out the risk of splitting the spine in a future baby, you’ll need to undergo a second-trimester screening.
Among other things, there is approximately 1% probability of detection of placental mosaicism. This is a condition in which some cells of the placenta contain a normal set of chromosomes, and some cells have anomalies. In such a situation, doctors advise to undergo an amniocentesis to find out whether there are such anomalies in your unborn child.
How to Tell Whether You Need a Chorionic Villus Sampling?
A biopsy of the chorion villi is accompanied by a risk of miscarriage. That’s why a pregnant woman should think twice before doing this test. Think whether its results will change your attitude to pregnancy.
Some women (or couples) understand that they are not ready to take care of a child with congenital diseases. They prefer to terminate pregnancy if a future child has a serious illness. If this is your case, then it is better to make a biopsy and be sure that everything is going well.
But if you have not decided what to do in such a difficult situation, the CVS pregnancy test will help you make your decision.
Some women decide to give birth to a child in any case, regardless of the results of the surveys. If this is about you, then it’s up to you to decide whether you need to do the CVS pregnancy test. Keep in mind that information about your child’s health, obtained with the help of a biopsy or amniocentesis, will help to prepare morally and materially for the birth of a child with this or that deviation.
You can refuse making the CVS pregnancy test if its results do not affect your decision to become a mother.
If it’s hard for you to decide on your own, consult a geneticist.
Does CVS Increase the Risk of Miscarriage?
After making the CVS pregnancy test, a miscarriage occurs in about one case out of 360. But not all specialists agree with this figure. Many believe that the procedure is much less likely to provoke miscarriage.
You can ask about the statistics of miscarriages after the CVS pregnancy test at the center where you make the test.
How to Reduce the Risk of Miscarriage?
Consult a geneticist and find out if there is a real need for the CVS pregnancy test for you personally. Perhaps the risk of abnormalities in your child is not so great as to expose the pregnancy to a small, but still, a threat.