Chorionic villus sampling

The purpose of this leaflet is to provide the patient with information on the goal, nature and risks of chorionic villus sampling.               

Chorionic villus sampling is offered to pregnant woman whose primary screening results (OSCAR test, NIPTIFY, Panorama, double test) indicate an increased risk of having a child with a chromosomal abnormality or who have a family history of a genetic disorder.

Chorionic villus sampling is voluntary and you have the right to decide whether you would like to have the test. You will be asked to sign a consent form before the test.

Please allow two to three hours for your appointment.

How is chorionic villus sampling performed?

Chorionic villus sampling involves removing a sample of chorionic villi (growing placenta) for testing. The chromosomes of the cells in the chorion are the same as those of the foetus. To examine these cells, a small tissue sample is taken from the growing placenta with a thin needle through the abdominal wall under ultrasound guidance. The tissue sample is then sent to the laboratory for examination.

When is the best time to undergo chorionic villus sampling?

Chorionic villus sampling is usually performed starting from week 12 of the pregnancy; however, it can be performed later. The safest time to undergo chorionic villus sampling is between 12 and 13 weeks of the pregnancy.

Does the procedure hurt?

The procedure can cause discomfort, but most women do not find it more painful than having a blood test. It is normal to have some spotting and cramping following the test. If you experience heavy bleeding, contact your doctor immediately.

What are the risks of chorionic villus sampling?

Chorionic villus sampling is a common test and complications are rare. For most women, the information obtained as a result of the test far outweighs the risks of the procedure.

  • Chorionic villus sampling increases the risk of miscarriage by 1-2%. Most pregnancies continue without issues.
  • To prevent infection, chorionic villus sampling is performed under sterile conditions; however, inflammation may occur on rare occasions in the form of fever, uterine contractions and abdominal pain.
  • In Rh-negative women, chorionic villus sampling carries the risk of foetal blood cells entering the woman’s bloodstream, leading the body to produce antibodies to fight them. To prevent this, the pregnant woman is given an injection of antibodies after the test, which reduces the risk of Rh incompatibility.
  • Sometimes the sample of cells removed during chorionic villus sampling may not be suitable for testing. This is less common with amniocentesis. In this case, chorionic villus sampling is repeated or amniocentesis (amniotic fluid testing) is offered.
  • With chorionic villus sampling, there is a rare chance of false negative results.

Results of chorionic villus sampling

The results of chorionic villus sampling come back within a few weeks after the procedure. The results will be communicated to you over the phone. Chorionic villus sampling will give you information about the presence of the condition being tested for. If the results indicate that the foetus has a genetic disease, the results of the test as well as the diagnosis outlook will be explained to you. According to Estonian law, the termination of pregnancy on medical grounds is allowed until the end of the 21st week of pregnancy. If you decide to terminate your pregnancy, contact your doctor or midwife for more information.

Please note

If you experience severe abdominal pain, bleeding, excessive discharge or fever after the procedure, you should immediately seek emergency care at the Women’s Clinic.


Approved by the decision of the Care Quality Commission of East Tallinn Central Hospital on 14.09.2022 (protocol no. 13-22)