Chorionic Villus Sampling (CVS)
After cleansing the skin of the maternal abdomen with an antiseptic solution, this involves guiding a fine needle under ultrasound guidance into the placenta (afterbirth). A small sample of the placenta is then taken off into a syringe and sent for testing.
What are the risks of CVS?
The main risk is from miscarriage which occurs in about 1-2% of pregnancies following CVS. There is an increased risk of facial abnormalities and limb defects in pregnancies where early CVS has been performed before 10 weeks.
There is also a risk of abdominal cramps and vaginal bleeding but if mild this does not usually cause any problems and you can take paracetemol safely for the cramps. If there is heavy bleeding, severe pain, fever, vaginal discharge or vaginal fluid loss you should contact your midwife, hospital, GP or our centre.
Why do you need to know my blood group?
Women who are Rhesus Negative need an injection of anti-D within 72 hours to protect their baby against the development of antibodies in the mother which can cause anaemia and jaundice in the fetus.
When is CVS done and who will do the test?
CVS is performed after 10+3 weeks in our centre and after 11 weeks in most NHS hospitals. All CVS tests are carried out in our centre by Dr Bryan Beattie, Consultant in Fetal Medicine, who has performed over 500 CVS procedures in Cardiff.
What tests are done on the sample?
Three main chromosome tests applied to the fluid are a PCR, a conventional karyotype and an array CGH.
1) The PCR works in 98% cases to give a result within 3 days for Down Syndrome (Trisomy 21), Edward Syndrome (Trisomy 18), Patau Syndrome (Trisomy 13) and if requested the sex of the baby.
2) A karyotype takes about 14 days and will identify most of the rarer chromosomal problems not picked up by the PCR.
3) Array CGH will identify up to 10% more chromosomal abnormalities that would not be picked up by a PCR and karyotype. This is the most accurate test and ideally we would advise this in all cases.
We also test for the dF508 cystic fibrosis genes which are responsible for about 85% of cases of cystic fibrosis.
Sometimes the CVS may fail to give a result, give a result which is difficult to interpret or an unexpected result and if so it will be explained to you what implications this may have for the baby.
What do I do before and after the test?
The procedure requires no special preparation and takes about 20 minutes. Ideally try to arrange for someone else to drive you home. After resting for about 5-10 minutes you can go home to rest for at least 24 hours. You should book time off work the next day and try to arrange for help if you have small children to look after.
How will I get the results?
This will be discussed at the time of the CVS but will usually be by phone followed by a report posted to you, the hospital and your GP.
When will I get my results?
Patients who have had an amniocentesis or CVS can ring the office weekdays on 0345 230 3386 just before 1600hrs for verbal results of the PCR according to the schedule below but about 2% of PCRs fail and we have to wait 2 weeks for the full results. Full written reports will be posted within a week. The office phones close at 1600hrs
Amnio / CVS Monday – Results Thursday
Amnio / CVS Tuesday – Friday
Amnio / CVS Wednesday – Monday
Amnio / CVS Thursday – Tuesday
Amnio / CVS Friday – Thursday
Amnio / CVS Saturday – Thursday