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Chorion villous sampling

Chorionic villous sampling is an invasive procedure in which under a constant ultrasound control the chorion (the precursor of the placenta) is punctured with a special needle and a syringe.



The aim is to obtain a certain amount of villi which are sent for subsequent laboratory genetic analysis.


Chorionic villous sampling is usually performed between 11+0-13+6 years.


The procedure is relatively painfree, takes about a minute to be performed, does not require any special preparation and does not cary any practical risk for the pregnant woman.


The obtained material (chorionic villi) is sent for laboratory analysis. The results are usually ready in about 1 to 3 weeks according to the type of the analysis performed. When a DNA (PCR) analysis is carried out the most common chromosomal abnormalities of the fetus can be ruled out in up to 5 working days.


In chorionic villous sampling the risk of a miscarriage is increased to about 0.5-1%. This means in a group of a 100 to 200 pregnant women undergoing the procedure, one procedure-related miscarriage will be observed. This is the reason why invasive prenatal diagnosis should be performed for a strict indication and only after a written consent from has been signed by the pregnant woman.


The differences between an amniocentesis and a chorionic villous sampling (CVS) are as following:

  • Gestational age at performing - CVS is carried out in the first trimester (11-13+6 years), while amniocentesis in the second (after 16+0 years);
  • Obtained material - in CVS the precursor of the placenta (chorionic villi) is sent for analysis, while in amniocentesis - the amniotic fluid;

In about 1% of the CVS cases it is difficult to have a conclusive prenatal diagnosis due to the presence of a condition called placental mosaicism (in these cases the placenta is genetically abnormal, while the fetus is not). This requires performing an amniocentesis at a later stage (after 16 years) in order to exclude genetic abnormality of the fetus.


Anti-D gamma-globulin injection is administered if the patient is rhesus negative.


For more information regarding the possibilities of having a chorionic villous sampling at MC MARKOVS, please contact your doctor or call at the registration desk.