Chorionic Villus Sampling (CSV)
A CVS is an ultrasound guided procedure which is performed to obtain a sample of placental tissue from which the baby develops.A CVS is best performed at around 12 weeks of gestation. The placental tissue which is tested is almost always the same chromosomaland genetic material as the baby, however, in a very small number of cases (1-2%) a discrepancy may exist which could require further testing.
- If you have received a screen positive result on the NIPS (cell free DNA) screening.
- If on ultrasound an increased nuchal translucency was detected (greater than 2.5mm)
- If you have received an increased combined first trimester screening result for Trisomy 21 (Down syndrome), Trisomy 18 (Edward’s syndrome) or Trisomy 13 (Patau syndrome).
- If any abnormality has been detected on ultrasound.
- If you have previously had a child with a chromosomal abnormality or birth defect.
- If there is a family history of genetic disease.
- If your requesting doctor has referred you for any other reason.
- If you are 35 years or older at the time of delivery, there is an increased risk of chromosomal abnormalities.
Prior to the CVS being performed, an ultrasound is done to check that the baby’s heart beat can be seen clearly, and the position of the baby is suitable for the sample to be collected. Our Doctor performs the majority of CVS procedures trans-vaginally.
A speculum is inserted into the vagina (like when you have a pap smear performed) and antiseptic is used to clean the vagina and cervix. Under ultrasound guidance a very thin metal tube (called a cannula) is passed through the cervical canal, through the neck of the womb and into the developing placenta. A small amount of the placental tissue is aspirated into syringe and removed.
If the sample amount is adequate for testing, the procedure has been successful and the cannula and speculum are removed. A second aspiration may be necessary if the first sample is insufficient. After the procedure for reassurance our Doctor will perform another ultrasound to show you your baby’s movement and heartbeat.
Although the CVS is a relatively safe procedure there is still the risk of miscarriage involved. This risk of miscarriage is approximately 1:500 - 1:1,000* caused by the procedure alone and is usually related to infection or mechanical reason.
If miscarriage is caused by infection, this usually occurs within 2 weeks of the procedure. The 1:500 - 1:1,000* risk of miscarriage is in addition to the ‘background risk’ of miscarriage. As with all pregnancies there is an inherent chance of miscarriage, which is more common in the earlier stages of pregnancy and especially in pregnancies where there are reasons for further procedures such as CVS.
Women with a Rhesus negative blood group may require an injection of anti-D post procedure, to protect a woman from developing antibodies against the fetus whose blood group may be Rhesus positive.
The small sample of placental tissue collected at the procedure is sent to a laboratory for either a banded karyotype analysis or micro-array molecular karyotype analysis.
The cells from the specimen are harvested and cultured and provide us with detailed genetic information about your baby. Please feel free to discuss these options with one of our Genetic Counsellors.
The results of a chorionic villus sampling are one of the most reliable tests. Keeping in mind that placental tissue is being analysed. Despite all care, human or laboratory errors can occur, so results are never foolproof. Accuracy is at or above 99%.
No. Despite so many advances in genetic testing, there are still many abnormalities that are not detected. Most major chromosomal abnormalities can be detected and now with the microarray testing being available we are able to detect many more genetic conditions that are caused by either extra or missing segments of DNA. There are also structural abnormalities that may be detected which are not genetically related.
Please feel free to discuss the testing options with one of our Genetic Counsellors or the Doctor performing your procedure.
Once the sample arrives at the laboratory the cells are cultured (grown under controlled conditions), analysed and then reported. Both the full karyotype or full molecular karyotype are available in around 7 to 10 working days.
The laboratory do offer a rapid result which is called a FISH (Fluorescent In Situ Hybridisation). The FISH test analyses for Down Syndrome (Trisomy 21), Edward’s Syndrome (Trisomy 18), Patau Syndrome (Trisomy 13), (22q deletion), DiGeorge Syndrome and any anomalies with the sex chromosomes (X and Y). The FISH results are usually available with 24-48 hours, however, the laboratory do charge an additional fee for the FISH test, please discuss this with the Genetic Counsellor or Doctor prior to the procedure.
There is no physical preparation required for CVS. However, it is important to have a copy of your blood group with you on the day of the test. Women who have a Rh negative blood group require an injection of Anti-D after the procedure. Anti-D can prevent the mother’s antibodies crossing the placenta and damaging the baby’s red blood cells.
It is recommended that you have someone to drive you home after your procedure. You should rest for about 48 hours after the procedure. It isn’t necessary to have complete bed rest, but any lifting or any strenuous exercise is to be avoided. Medical certificates can be arranged for both you and your partner if you require time off from work or study.
Slight cramping and possible spotting is not uncommon after the procedure, but if you start to experience any severe cramping or there is excessive fluid loss, you should contact your Doctor.
Our Genetic Counsellor will work very closely with you and your referring Doctor to ensure you are supported through any abnormal result. We will provide you with as much information about all options available to you.