Chorionic villus sampling (CVS) involves taking a sample of cells from the tissue of the placenta of a pregnant woman. These cells are called chorionic villi.
The procedure is always carried out under the guidance of an ultrasound scan to avoid making a hole in the amniotic sac (the protective sac that cushions the baby with fluid as it grows).
Two different methods can be used during the procedure:
- transabdominal CVS
- transcervical CVS
Transabdominal CVS
During transabdominal CVS, your tummy is cleaned with antiseptic and a needle is inserted through your tummy and abdomen wall. The needle is guided towards your womb using the image on the ultrasound scan.
Attached to the needle is a syringe, which is used to extract a small sample of chorionic villi, after which the needle is removed.
Transcervical CVS
During transcervical CVS, the chorionic villi are collected through your cervix (the lower part or neck of the womb).
First, your vagina and cervix will be cleaned with antiseptic. A tube is inserted through your vagina and cervix, and is guided toward the chorionic villi using the ultrasound scan. Gentle suction is used to remove a small sample of the chorionic villi. The tube is then removed.
Which method?
The choice of whether to used transabdominal CVS or transcervical CVS depends on where your placenta is. One method may be able to reach the chorionic villi better that the other.
Transabdominal CVS may be slightly safer than transcervical CVS, but there is no difference in the rate of miscarriages between the two methods.
Transcervical CVS is much less commonly used than transabdominal. It can be harder to obtain a sample using this method, and the tube may need to be inserted more than once. Transcervical CVS is also more likely to cause vaginal bleeding immediately after the procedure. Bleeding occurs in about 10% of women who have this procedure.
Is CVS painful?
CVS has been described as being uncomfortable, rather than painful. Transcervical CVS is comparable to having a smear test. The cramps that some women experience afterwards are about as painful as menstrual cramps.
Some women who have transabdominal CVS report having a sore abdomen after the procedure and there may be some vaginal bleeding.
One study of pain during CVS found that transabdominal CVS may be more painful for larger women because their abdominal wall is thicker. Transcervical CVS may be more painful for women who have not previously given birth. In some cases, painkilling medication in the form of a local anaesthetic can be used to numb the area.
How long does it take?
CVS usually takes around 20 minutes to perform. Afterwards, you will be monitored for anything up to an hour in case the test causes any reactions, such as heavy bleeding. You will then be allowed to return home to rest.
After the procedure, you may experience cramps that are similar to menstrual cramps, and "spotting" (drops of blood from your cervix). You may wish to avoid any strenuous activity for a day or two.
The first results of CVS should be available within a few days, and this will tell you whether a major chromosome problem has been discovered.
The full results, including smaller, rarer conditions, can take two to three weeks to come back. If the test is looking for a specific disorder, the results may take up to a month.
Recovery
Recovery from CVS should take about a day. Some people may experience bleeding or cramps after the procedure. Contact your GP for advice if, after CVS, you have:
- a high temperature of 38C (100.4F) or over
- excess bleeding
- excess vaginal discharge
