What is Chorion Villus Sampling Biopsy?

Chorionic Villus Sampling biopsy (CVS) involves examination of the placenta. Both the fetus and the placenta come from the same fertilized egg (zygote) and thus the chromosomes present in the placenta cells are the same as the ones of the embryo. Therefore, it can be checked whether your fetus has any genetic or chromosomal conditions, such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18) or Patau syndrome (trisomy 13).

When is a Chorion Villus Sampling - CVS recommended?

Trophoblast biopsy is not recommended for all pregnant women. It is only recommended if your baby is at high risk of having a genetic or chromosomal condition.

This may be due to the following reasons:

• Nuchal translucency scan has shown that your baby may be born with a condition such as Down Syndrome, Edwards Syndrome or Patau Syndrome.
• You had a previous pregnancy in which a genetic disorder was identified (e.g. skeletal anomalies).
• You have a family history of genetic disorders such as sickle cell disease, thalassemia, cystic fibrosis or muscle dystrophy.

Which diseases can CVS diagnose?

• Down Syndrome (Trisomy 21) - all children born with Down Syndrome have some degree of learning disability and mental retardation, but this varies considerably among children.
• Edwards Syndrome and Patau Syndrome - condtions that can lead to miscarriage, mortality or severe learning disabilities. These pregnancies are rarely come to a delivery.
• Thalassemia - (a condition that affects the red blood cells, which can cause anemia, restricted grawth and organ damage).
• Sickle cell disease - (erythrocytes develop abnormally and are unable to properly transmit oxygen around the body).
• Cystic fibrosis - a condition where the lungs and gastrointestinal system produce and are blocked by a thick sticky mucus.
• Phenylketonuria - (your body cannot break down a substance called phenylalanine, which can reach dangerous levels in the brain).
• Duchenne muscular dystrophy - (a condition that causes progressive muscle weakness and disability).
• Many other genetic syndromes.

How is CVS made?

Local anesthesia is administered first. Then, a thin needle passes through the mother's abdominal walls, enters the uterus and a sample is drawn. The path of the needle is carefully monitored and performed under ultrasound guidance.

The preparation itself takes about 10 minutes, the invasive procedure takes 1-2 minutes, then the fetal heart rate is checked. The whole counselling may take about 30 minutes.

What should I wait for?

The CVS procedure is usually described as unpleasant and not painful, although you may experience some cramps that are similar to period pain for a few hours afterwards.

For the first two days you may notice some discomfort, period pain or a little vaginal bleeding. These are relatively common and in the vast majority of cases pregnancy continues without problems. You can get simple painkillers like paracetamol.

If you have severe abdominal pain, vaginal bleeding, or if you develop fever or chills seek medical advice.

When can I expect the results?

Results for Down Syndrome (Trisomy 21) and other major chromosomal abnormalities are usually available within the first 3 days. Results for rare genetic abnormalities or suspected syndromes can last up to 2-3 weeks. Once we receive the results, we will call you in order to discuss them with you.

Unfortunately, there is no cure for most of the conditions diagnosed by CVS, so you should carefully consider your options.

You may decide to continue your pregnancy by collecting information about the condition so that you are fully prepared.

Will the procedure need to be repeated?

In about 1% of cases, the invasive test should be repeated because the results are not clear.

What are the risks associated with the test?

The risk of miscarriage due to CVS is about 0.3-0.5% and this is the same as the risk of amniocentesis at 17-23 weeks of gestation. If a miscarriage is to occur as a result of the examination, this will occur within the next three days.

Some studies have shown that when CVS is performed before the 10th week of the pregnancy there is a small risk of abnormalities in the fingers and toes of the fetus. To avoid this risk we never perform CVS before the 11th week of the pregnancy.

Insufficient sample

In about 1 in 100 procedures, the sample of cells obtained may not be suitable for examination. This could be due to the fact that not enough cells were obtained or because the sample was infected with cells from the mother. If the sample is inadequate, the CVS may need to be performed again or you could wait a few weeks for amniocentesis.

Contamination

As with all types of surgery, there is a risk of infection during or after chorionic biopsy. However, serious infection occurs in less than 1 in every 1,000 cases.

Rhesus sensitisation

If your blood type is Rhesus (RhD) negative but the fetal blood type is RhD positive, sensitisation may occur after CVS.

This is because even a small amount of fetal blood enters the mother's bloodstream and your body begins to produce antibodies, which if untreated, can cause the fetus to self-damage its red blood cells. If you do not already know your blood type and Rhesus, you should have a blood test in order to know this information before having your CVS to see if there is a risk of sensitisation. If necessary, an anti-D immunoglobulin dose may be administered to avoid sensitisation.