CVS: what it is, when it is performed and what the risks are

CVS is an invasive prenatal diagnosis technique that allows you to discover any fetal genetic and chromosomal abnormalities. In this article, we explain how, when and why this test is performed, what its risks are and how much it costs.

CVS  or  chorionic villus sampling  is an invasive  prenatal diagnosis  test , which is used to evaluate the presence of any  genetic or chromosomal abnormalities  in the fetus.

This test represents an alternative to amniocentesis , with the advantage that it can  be performed much earlier , thus allowing for an earlier diagnosis.

To date, CVS is generally performed only after screening tests (such as nuchal translucency, Bitest, or fetal DNA testing) report an increased risk of fetal abnormalities.

When is CVS performed and in which cases is it recommended?

^{According to the current indications of the Istituto Superiore di Sanità (ISS) ,} CVS can be performed  between the 10th and 13th ^week of pregnancy .

The examination is recommended when there is an increased probability of birth defects in the fetus and, in particular, if:

• screening tests , such as the Bitest or fetal DNA test , have shown a high risk of chromosomal alterations (such as Down syndrome);

• the first trimester ultrasound revealed the possible presence of malformations ;

• the expectant mother already has a child affected by a chromosomal anomaly ;

• one or both parents are carriers of chromosomal alterations or genetic diseases (such as thalassemia or haemophilia).

Furthermore, according to the ISS guidelines, CVS should also be offered “to women over the age of 35 who have not performed the prenatal screening tests required in the first trimester of pregnancy”. This is because the likelihood of having a child with chromosomal abnormalities tends to increase with maternal age.

What information can be obtained with CVS?

Chorionic villi sampling allows to identify:

• almost all chromosomal abnormalities , such as trisomy 21 (Down syndrome), trisomy 13 (Patau syndrome), trisomy 18 (Edwards syndrome), and sex chromosome abnormalities (such as Turner syndrome);

• numerous genetic diseases , such as thalassemia , haemophilia or cystic fibrosis . The search for these pathologies, however, is not carried out automatically, but only at the request of the gynecologist in the presence of specific risk factors ;
• paternity of the fetus , always on specific request.

Is CVS a reliable test?

Since it is an invasive diagnostic test, villocentesis has a very high reliability , between  98 and 99% .

In the presence of  doubtful results (1-2% of cases),  the gynecologist will request an amniocentesis , which can be performed between the   16th  and ^18th week ^of pregnancy .

What are the risks of CVS?

This test is associated with a  1-2% risk of miscarriage  when performed abdominally (which is the safest technique), although  more recent studies  show  lower risk rates  .

Since the  operator’s ability  and experience  represent  crucial factors  for risk reduction, the advice is to contact  operators and structures  that perform this  routine procedure  (such as a tertiary hospital centre ).

Another risk may be linked to the onset of a uterine infection , a very rare occurrence that affects  less than one in a thousand women . In any case, in the presence of symptoms such as:

• fever
• severe abdominal pain
• copious loss of blood  or  fluid

it is important  to immediately contact your trusted gynecologist or go immediately to the emergency room .

Finally, it should be emphasized that performing CVS  before the 10th ^week exposes  the child to a  greater risk of complications . For this reason, current guidelines state that this test should not be done too early in pregnancy.

CVS or amniocentesis: which one to choose? 

Both procedures have their pros and cons. CVS has the advantage of being able to be performed earlier and also allows you to have results more quickly .

In the event of serious congenital anomalies, therefore, the couple may decide to proceed with the termination of pregnancy at an earlier stage, helping to reduce stress from both a physical and psychological point of view.

On the other hand, some studies document a slightly increased risk of miscarriage. In addition, in 1-2% of cases , chorionic villus sampling produces questionable results and still requires the execution of an amniocentesis.

In any case, to decide which examination to perform, it is advisable to always rely on your trusted gynecologist , who will evaluate the most suitable technique for the specific clinical situation and the needs of the couple.

How is CVS performed and how long does it take?

The examination consists in taking some fragments of the  chorionic villi , i.e. the tissue from which the placenta will form  , which are sent to a specialized laboratory to be analysed.

The procedure takes place in a hospital environment under ultrasound control and involves inserting a needle  through  the abdominal wall  or, more rarely,  vaginally (for example in the case of a retroverted uterus).

The sampling takes about  5-10 seconds  , and the entire procedure usually takes  between 30 and 45 minutes . One hour after the examination, an ultrasound scan is performed to check the heartbeat of the fetus.

Is CVS painful?

Chorionic villus sampling can be  uncomfortable  or cause  slight pain , but it is usually well tolerated and for this reason it is often performed without anesthesia.

After the procedure, there may be  small vaginal losses of blood  or  liquid or slight  contractions , which tend to resolve spontaneously or with the intake of antispasmodic drugs (to relax the uterine muscles), which will be prescribed by the doctor if necessary .

How to prepare for the exam?

Blood group check

To perform chorionic sampling, it is necessary to know the blood group and Rh factor of the future mother and, if Rh negative , also check the blood group and Rh factor of the future father .

If the paternal Rh is positive , the mother with Rh negative will have to perform an indirect Coombs test before undergoing CVS. Furthermore, after the examination, an injection of immunoglobulins will be performed , called anti-D prophylaxis , in order to avoid the possible formation of maternal antibodies against the baby’s red blood cells.

Antibiotic prophylaxis

With the exception of some special cases, it is not recommended to take antibiotics in the days before (or after) the procedure. 

How to behave after CVS?

After the procedure, it is good to  rest , avoiding  sexual intercourse  and  strenuous physical activity  for about  24-48 hours .

When are the results communicated?

Wait times vary based on the objective of the exam. For  chromosomal abnormalities , such as Down syndrome, results are reported within  3 to 10 days .

In the case of some  genetic diseases , on the other hand, the result can take up to  2 or 3 weeks .

How much does CVS cost?

With the National Health Service , CVS is  free  for all women (regardless of age) who have a  high risk of congenital anomalies of the fetus .

Alternatively, this examination can be performed at  private facilities , with a cost between  1,000  and  1,800 euros .