Chorionic villus sampling - What happens during chorionic villus sampling

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 continuous guidance of an ultrasound scan to ensure that nothing enters the amniotic sac (the protective sac that cushions the baby with fluid as it grows) or touches the baby.

CVS can be carried out using two different methods:

transabdominal CVS
transcervical CVS

In most cases, the transabdominal technique is used.

Transabdominal CVS

During transabdominal CVS, your tummy is cleaned with antiseptic, you are given a local anaesthetic injection and a needle is inserted through your skin into the womb. The needle is guided towards the placenta 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 the sample is removed, the needle is taken out.

Transcervical CVS

During transcervical CVS, a sample of 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 thin tube or forceps (smooth metal instruments that look like large tongs) are then inserted through your vagina and cervix, and are guided toward the placenta using the ultrasound scan.

Which method will be used?

The transabdominal method is preferred in most cases. This is because it can be harder to obtain a sample using the transcervical 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, which occurs in about one in every 10 women who have this procedure. There is, however, no difference in the rate of miscarriages between the two methods.

Transcervical CVS may be preferred to transabdominal CVS if it is easier to reach your placenta this way.

Is CVS painful?

CVS is usually described as being uncomfortable, rather than painful.

In most cases an injection of local anaesthetic will be given before transabdominal CVS to numb the area where the needle is inserted, but you may have a sore tummy afterwards.

Transcervical CVS feels similar to having a cervical screening test.

How long does it take?

The procedure itself usually takes around 10 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 can then go home to rest.

Recovery

After the procedure, it is normal to have cramps that are similar to menstrual cramps and light vaginal bleeding called 'spotting' for a day or two. You can take over-the-counter painkillers, such as paracetamol (but not NSAIDs such as ibuprofen or aspirin), if you experience any pain.

You may wish to avoid any strenuous activity for a couple of days.

Contact your midwife or the hospital where the procedure was carried out for advice as soon as possible if you develop the following symptoms after the procedure:

a high temperature of 38°C (100.4°F) or more
chills or shivering
heavy vaginal bleeding or discharge
contractions

Getting the results

The first results should be available within a few days, and this will tell you whether a major chromosome problem has been discovered.

If rarer conditions are also being tested for, it can take two to three weeks to come back. If the test is looking for a specific disorder, the results can take up to a month.