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Chorionic villus sampling (CVS) is one of the invasive prenatal tests that can detect genetic defects in the fetus. Such a test may be ordered by a doctor when he or she decides that there are indications for it. When is chorionic villus sampling recommended and what is it about. What is the risk of complications?
Prenatal tests – invasive and non-invasive
Chorionic villus sampling (CVS) belongs to the group of invasive prenatal tests. It consists in taking a fragment of the amniotic membrane, i.e. chorion, by the transvaginal or transabdominal route under local anesthesia. The procedure requires continuous ultrasound control.
Invasive tests performed in the prenatal period are the most reliable form of diagnosis and therefore can be the basis for diagnosis. However, they are associated with greater interference in the pregnant woman’s body, as well as the risk of miscarriage. In the case of chorionic villus sampling, the probability of complications is 2–3%. Despite the risk, it is invasive tests that give almost one hundred percent certainty that the result is accurate. The other invasive and invasive prenatal tests are amniocentesis and cordocentesis.
Prenatal diagnosis involves not only risk-bearing tests, but also completely safe non-invasive tests, including pregnancy ultrasound, as well as PAPP-A, Harmony and SANCO tests. It is these methods that are best used in the first place for diagnostic purposes. Ultrasound is completely safe for the pregnant woman and the fetus, as is taking a blood sample from the expectant mother. If the results indicate a high risk of fetal malformations, the doctor should order tests that are more invasive.
- Read more about SANCO and Harmony non-invasive prenatal testing.
What anomalies does CVS detect?
The chorion is the fetal membrane that forms the placenta. During the biopsy, a fragment of it is collected, and the analysis can detect abnormalities such as Down’s, Turner, Edwards, Patau, Duchenne or Tay-Sachs syndromes. The test is used to diagnose cystic fibrosis, cystic fibrosis, haemophilia, sickle cell anemia and alkaptonuria.
In order to diagnose a specific medical condition, it is necessary to examine the sample for the correct angle. Proper targeting of the procedure makes it possible to compare the CVS test with family history and other fetal test results.
Contraindications for chorionic villus sampling
The chorionic villus sampling procedure is not performed in women before the 8th week of pregnancy, and in the case of procedures up to the 10th week, there is a greater risk of anatomical defects in the developing child. CVS is not performed when maternal anti-Rh antibodies are detected.
Pregnant women who test positive for HIV are also a special case. During chorionic villus sampling, there is a risk of infecting a child with a virus, therefore the possibility of implementing this prenatal test should be discussed with your doctor.
Other prenatal tests worth paying attention to include:
- NIFTY test – indications, results and price of the test
- PAPP-A test – what is it and how much does it cost?
Chorionic villus sampling – indications
Due to possible complications, chorionic villus sampling is performed if there are medical indications. Most often, they may be due to an abnormal image of the fetus obtained during ultrasound or positive results from screening tests such as the SANCO test. The prerequisite for chorionic villus sampling is pregnancy in a woman over 35 years of age or the disclosure of a genetic disease in a child born earlier.
Your doctor may recommend a chorionic villus sampling when there is a reasonable suspicion of a genetic defect in the fetus. However, CVS testing is performed during the first trimester of pregnancy, most often between 8 and 11 weeks of pregnancy. At the latest, chorionic villus sampling can be performed in the 14th week of pregnancy. If the suspicion of abnormalities appears later, we can choose amniocentesis (up to week 18) and cordocentesis (usually up to 23 weeks of pregnancy).
How is chorionic villus sampling performed?
We are going to the planned chorionic villus sampling procedure with a referral and medical documentation. The most important thing is the confirmed result of the mother’s blood type, and in the case of the presence of the Rh minus factor, also the Coombs test, measured in the two weeks before the biopsy.
Before chorionic villus sampling, the urinary bladder should be emptied. The doctor will also administer appropriate pharmacological agents and local anesthesia. The examination is performed under ultrasound guidance in one of two ways. The first is transabdominal biopsywhich involves inserting a needle through the abdominal wall. The second is transvaginal biopsyduring which the doctor inserts a catheter or special forceps through the cervix.
The duration of the procedure is on average 15-20 minutes. The sample taken during chorionic villus sampling is subjected to cytogenetic or more complex molecular examination. We wait for the results from several days to three weeks.
Complications after chorionic villus sampling
The main side effects of chorionic villus sampling in a pregnant woman include:
- slight bleeding;
- leakage of amniotic fluid;
- the occurrence of an intrauterine infection;
- development of clubfoot in the fetus;
- in Rh negative women, immunization may occur;
- spontaneous miscarriages that occur in just over 2-3% cases.