When is the test done;
The chorionic villous sampling test is performed between 11-15 gestational weeks.
Why is CVS needed?
The commonest indications are:
Increased risk for a chromosomal abnormality as calculated by the combined test (the combination of maternal age, ultrasound and biochemical markers) in the first trimester.
History of a genetic disease in the family.
Discovery, after ultrasound, of a congenital abnormality in the fetus.
The chorionic villous sampling procedure is a diagnostic test. It is done by collecting a very small amount of chorionic villi (the placenta tissue). In the vast majority of cases, but not always, the fetus and the placenta share the same genetic material and, therefore, chromosomes found in the placenta are the same as the ones found in the fetus.
How is the test done?
First, we clean with an anteseptic the tummy's skin. Afterwards, we numb the skin where the needle will insert with local anesthetic. Subsequently, a very thin needle passes through the tummy, into the uterus and, being directed to the placenta, a small area of the placenta is sampled. The needle is under continuous ultrasound visualisation. The whole procedure lasts for about 1- 2 minutes and at the end of the procedure the fetal heartbeat is checked. The following video demonstrates the procedure's technique.
What happens after CVS is done?
After we confirm that the fetal heartbeat is normal, the miscarriage risk decreases significantly. For the next 2- 3 days you might experience some symptoms like mild abdominal ache, period- like cramping and mild vaginal bleeding. These are quite common after CVS and you should not be really worried since, in most of the cases, pregnancy continues normally. In case you want to ease any symptoms, you can take simple painkillers like paracetamol either orally or as suppositories. In case you feel intense pain, experience heavy bleeding, or have fever, you need to contact us immediately or visit a hospital.
When are the results back?
The results are announced in two ways. The first results for Down's syndrome or other major chromosomal abnormalities come from PCR and are back in 2- 3 working days. In 99% of the cases, they are identical to the final ones. These results (the final ones) come from cell cultures and for the major chromosomal abnormalities are back in 2 weeks. Whenever we have the results, we will let you know immediately.
Does the procedure need to be repeated for any reason?
In about 1% of the cases, the test needs to be repeated because the results will be inconclusive. In other cases, there might be mosaicism of cells and this reslut needs to be confirmed by amniocentesis.
Are there any risks from CVS?
Luckily, the procedure- related risks are uncommon. There is a 1 in 100 chance of miscarriage caused by the test. This risk is the same as the one from amniocentesis at 16 weeks. If you were about to miscarry because of the procedure, this will happen in the next, few days. The risk goes down by 85% after the first 24 hours.
There is a 1 in 1000 chance of maternal infection. This is why we will disinfect the area with antiseptic and use, practically, sterile methods of performing the procedure.
Some studies have shown that if CVS is performed prior to 11 weeks, there is a small risk of abnormalities in the fetal extremities, therefore we avoid performing the procedure prior to this gestational age.