Chorionic villus sampling (CVS)

What is Chorionic villus sampling (CVS)?

This is a diagnostic test and involves examination of the chorionic villus (placental tissue). Both the baby and the placenta come from the same genetic material and so the chromosomes present in the placenta cells are the same as those of the baby.

When is this test performed?

Studies have shown that when chorionic villus sampling biopsies take place before 10 weeks, there is a small risk of structural abnormalities in the fetus, mainly in the upper and lower extremes. In order to eliminate this risk, the CVS test is not performed before 11 weeks of gestation, with a proposed maximum gestational age of 15 weeks.

How is the biopsy done?

Under ultrasound, the exact location of the placenta is assessed and local anesthetic is given to the skin. A very fine needle (biopsy needle) then passes through the skin of the mother’s abdomen and a sample of chorionic villus is taken from the placenta. The test lasts for a few minutes and immediately after we finish, we hear the heart of the fetus.

What should I expect after the biopsy?

It is expected for the first two to 24 hours to experience period pain or even pain in the lower abdomen. It is normal, as it is also normal to sometimes be described as a dappled vaginal bleeding. In many cases it helps to get a simple and safe painkiller tablet such as paracetamol (Depon). It is not normal to feel acute abdominal pain, have fever or vaginal bleeding. In all these cases, you should seek medical advice.

When are my results available?

The results for chromosomal abnormalities such as Down syndrome are usually available in two to three days (PCR). Fetal karyotype (cultivation) and information on other abnormalities / syndromes are available within 2 weeks of tissue receipt. Once we have the results we will contact you immediately.

Is this a 100% effective test?

Chorionic villus biopsy is a diagnostic test. However, in 0.5% of cases it may not be effective due to placental mosaicism. In this case the lab will ask for a repeat of an invasive test, usually an amniocentesis around 16 weeks of gestation.

What are the risks to the mother and the fetus from this test?

The risk of miscarriage as described in the international literature is about 1/1000 and is the same as the risk of miscarriage from amniocentesis. Miscarriage is due to an accident during the test and therefore if we are happy with the process and listen to the fetal heart rate immediately after the biopsy, we are relieved that everything went well. In any case, biopsy-associated miscarriage is expected within the next few days of the procedure.

A very low risk of maternal infection (1 in 1000) is described and therefore it is recommended to record the maternal temperature for the next two days. In case of fever, clinical evaluation and possible initiation of antibiotic therapy are recommended.