Leeds Fetal Medicine Unit Website

Chorionic Villus Sampling (CVS)

CVS is the removal of a small amount of placental (afterbirth) tissue for use in diagnosing chromosomal or genetic disease. It relies on the principle that the placental tissue usually has the same genetic profle as the adjoining baby. In Leeds prior to CVS an ultrasound of the developing fetus is performed to confirm gestation, identify any signficant abnormality and localise the placenta. Once this has been done CVS can be carried out after 11 weeks of pregnancy as long as the placenta is in a position to allow sampling through the abdominal (tummy) wall. After cleaning the abdomen local anaesthetic is instilled to numb the skin where the needle is to be inserted which is done under direct ultrasound visiion. Once in the correct area a sampling device is inserted through the needle and oscilated until enough placental fragments are obtained, this make take several attempts, but will only involve one needle insertion.

CVS being performed

Once the sample has been obtained it is sent to the laboratory at St. James, where it is rapidly processed to give a preliminary result usually within 24-48 hours and a final result in 18 days. The first (rapid) result from CVS looks at all pairs of chromosomes which can be useful if you or your family have a rarer form of chromosomal disorder (for example a translocation. In approximately 2% (1:50) of cases the rapid result obtained from CVS can provide confusing information (usually as a result of confined placental mosaicism), which may not accurately reflect the chromosome structure of the baby. If this occurs then we will let you know, but will have to wait for the long term result which will be available in 18 days. Very rarely the sample taken at time of CVS fails to "grow" in the laboratory, in these cases all that can be done is to repeat the test.

Following the procedure we check the patients blood group and take their contact details so that we can inform them by phone when the result is ready. If the patient is rhesus negative we give an injection of anti-D to prevent potential immunisation.

Patients are then allowed home. We do not recommend that patients drive themselves home following the procedure, but no special precautions need to be taken otherwise.

Important - Risks associated with CVS

Like any prenatal invasive procedure, CVS can potentially cause a miscarriage to occur. The national figure for this based on published research is 1%. This means that 1 in 100 procedures performed will cause a miscarriage to occur whether the baby has normal or abnormal chromosomes. It is unknown why this occurs, but may be related to infection. In our unit audit we audit our figures to determine what the miscarriage rate following the procedure is in our hands, click here to see our current results.

For furher information click here for an information sheet (in pdf format)

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