Chorionic Villus Sampling (CVS)
What is chorionic villus sampling?
Chorion villus sampling (CVS) involves the sampling of placental tissue using a needle that is passed through the maternal abdomen into the placenta. Both the baby and placenta (afterbirth) originate from the same cell and so the chromosomes present in the cells of the placenta are the same as those of the baby. The procedure is done transabdominally, we do not perform transvaginal CVS.
How is CVS done?
We use local anesthetic on the maternal abdomen (to anaesthetize the skin and soft tissue), but do not inject local anesthetic into the uterus. A thin needle is then passed through the mother’s abdomen and a sample of villi is taken. The procedure is done as an ultrasound guided technique. The needle can be seen constantly during the procedure. The amniotic sac is not punctured. The procedure lasts 1 minute. We check the fetal heart beat following the procedure and also make sure we have obtained a good sample for the genetic laboratory.
What should I expect after the CVS?
For the first couple of days you may experience some abdominal discomfort, period-like pain or a little bleeding. These are relatively common and in the vast majority of cases the pregnancy continues without any problems. You may find it helpful to take simple painkillers like paracetamol 40 minutes before the procedure. If there is a lot of pain or bleeding or if you develop a temperature please seek medical advice.
When can I expect to get the results?
The results for Down’s syndrome and other major chromosomal defects are usually available within 3-4 working days (FISH or PCR test). For a full culture that would exclude rare defects, the villi need to be cultured first and a final result takes 2-3 weeks to obtain. We contact you with the results as soon as they are available.
Will the procedure need to be repeated?
In approximately 1% of cases the invasive test will need to be repeated because the results are inconclusive.
What are the risks associated with the test?
The risk of miscarriage due to CVS for our unit is 0.3% (1:300 risk for miscarriage) over and above the spontaneous loss rate of 2% at 11-14 weeks. This is the same risk from amniocentesis at 16 weeks. If you were to miscarry due to the test, this would happen within the first five days following the procedure. We do not perform CVS before 11 weeks due to the small risk of abnormality in the baby’s fingers and/or toes.