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What is Chorionic Villus Sampling (CVS)?
CVS is an invasive prenatal diagnostic procedure. It involves removing a small sample of chorionic villi, which are tiny projections of placental tissue. These cells contain genetic material that can be examined for certain chromosomal or inherited conditions.CVS is generally offered when there is an identified or increased risk of a particular genetic or chromosomal condition. The procedure is usually carried out between 10 and 13 weeks of pregnancy, although the exact timing may depend on the individual clinical circumstances.
CVS can provide early diagnostic information when there is an increased risk of a genetic or chromosomal condition, helping families understand their options.
Why is CVS Recommended?
A doctor may discuss CVS when there is a higher-than-usual possibility of a genetic or chromosomal condition. Some common reasons include the following:- Family history: There may be a known inherited genetic condition in the family
- Previous affected pregnancy: A previous pregnancy may have been affected by a genetic or chromosomal disorder
- Screening results: Prenatal screening may indicate an increased risk of a chromosomal condition
- Known genetic risk: Parents may already have information suggesting a higher chance of a particular inherited condition
How is Chronic Villus Sampling Performed?
Chorionic villus sampling (CVS) is performed under continuous ultrasound guidance. There are two main ways of obtaining the placental sample, which include the following:Transabdominal CVS
In transabdominal CVS, the mother lies comfortably while an ultrasound scan is used to locate the placenta and identify a safe route for collecting the sample.- The skin on the abdomen is cleaned, and a local anaesthetic may be used to numb the area
- A thin needle is then carefully inserted through the abdominal wall and into the placenta while being monitored with ultrasound
- A small amount of chorionic villus tissue is collected through the needle
- Once the sample has been obtained, the needle is removed, and the tissue is sent to a laboratory for testing
Transcervical CVS
In transcervical CVS:- A thin instrument is passed through the vagina and cervix to reach the placenta
- Ultrasound guidance is used to help position the instrument safely and collect a small tissue sample
- The method mainly depends on the position of the placenta and which approach is considered safest and most suitable for the individual pregnancy
What Can Women Expect After CVS?
Some women may experience mild abdominal cramping or discomfort after the procedure. The treating doctor may provide specific instructions about activity and symptoms to watch for after the CVS.Because CVS is an invasive procedure, it carries a small risk of complications. Miscarriage is one of the important risks that should be discussed before the procedure. The individual level of risk may vary depending on the circumstances and the technique used. Women should discuss any concerning symptoms after CVS with their doctor rather than relying on general advice.
How is CVS Different From Prenatal Screening?
One important distinction is that CVS is a diagnostic test, whereas many commonly performed prenatal tests are screening tests. Screening tests estimate the likelihood of certain conditions but do not usually confirm whether the baby has a particular genetic or chromosomal condition. CVS, when used for the relevant condition, can provide more definitive diagnostic information.However, CVS does not test for every possible genetic condition or birth defect. The conditions assessed depend on the clinical indication and the laboratory tests requested.
The CVS provides important diagnostic information early in pregnancy when the risk of genetic or chromosomal disorder is high. As this is an invasive procedure, the decision about whether to undergo it necessitates proper counselling regarding the purpose of the procedure, the limitations of CVS, and the possible risks involved. Parents thinking about CVS should consult with their gynaecologist and, at times, also with a genetic counsellor, taking into consideration their individual situation.
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FAQs on Chorionic Villus Sampling: Why and How Is It Performed?
- Is CVS painful?
CVS is not usually painful, but it can cause mild discomfort, pressure, or cramping during and after the procedure. Most women tolerate it well, especially because it's performed under local anaesthesia. Severe or persistent pain should be reported to the doctor. - What genetic defects can be detected through CVS?
CVS can detect certain genetic and chromosomal conditions, including Down syndrome, Edwards syndrome, Patau syndrome, cystic fibrosis, sickle cell anaemia, thalassaemia, and other inherited disorders. The specific conditions tested depend on the family history, pregnancy risk, and genetic tests selected. - How is CVS different from amniocentesis?
CVS examines the placental tissue and is usually performed around 10-13 weeks, while amniocentesis examines the amniotic fluid and is performed after 15 weeks. Both can identify certain genetic and chromosomal conditions but differ in timing, sample type, and procedure.