Chorionic Villus Sampling (CVS)
Chorionic villi are small thread-like projections that make up part of the early placenta. Cells of the chorionic villi almost always have the same chromosomes as the fetus. Therefore, abnormalities in the chromosomes of the chorionic villi are also found in chromosomes of the fetus.
Some of the reasons for choosing to have a Chorionic Villi Sampling (CVS) include having an increased risk of having a baby with a chromosome abnormality, the most common being Down syndrome. This could be because of the age of the mother or because the result of a prenatal screening test (nuchal translucency) indicates that the fetus has in increased risk of an abnormality.
A CVS would also be offered when either parent has a family history of a genetic disorder that can be diagnosed prenatally eg cystic fibrosis, muscular dystrophy.
A CVS is performed from 12 weeks. The test involves taking a sample of the developing placenta that contains the chorionic tissue. Before the test is performed, an ultrasound scan is carried out to check your dates and the position of both the baby and the placenta.
The skin on the abdomen is cleaned with antiseptic and a local anaesthetic injection is given to numb the area. Under ultrasound guidance, a fine needle is then passed through the wall of the womb into the chorionic tissue. A small piece of the chorion tissue (about the size of a few grains of rice) is removed through the needle and sent to the laboratory for testing.
Most women describe the procedure as uncomfortable rather than painful, similar to period pains. They say they are aware of a “pushing” feeling and some soreness over the area afterwards.
The test itself only takes a few minutes, though we schedule you a one hour appointment. This includes a consultation where you will be given information regarding the CVS, your questions answered, the initial ultrasound and the CVS itself. After the procedure, you will be rescanned to ensure no problems have occurred.
If your blood group is Rhesus negative, you will be given an injection following the procedure to prevent formation of antibodies in your blood, which may affect future pregnancies.
We encourage you to bring a companion with you for support during and after the test. Afterwards, we suggest you take things easy for a couple of days, avoiding any heavy lifting or strenuous exercise.
It is not unusual to have some spotting for a few hours after the test. The “period pain” feeling may persist for 24-48 hours. This is not unusual and should settle after rest and paracetamol, which is safe to take in pregnancy. 1% of women who have had an amniocentesis or CVS will experience a small amniotic fluid loss (leak) or bleeding.
This is usually of no concern and will normally cease within 48 hours. If this happens to you please:
• Rest in bed for 48 hours
• Do not have a bath (showering is fine)
• Do not have sex
• Call Dr Carmody’s rooms on 3371 4933. We will book an appointment for a scan 48-72 hours after the procedure.
If you experience severe pain, blood loss or large gush of fluid out of our office hours, please proceed to your closest hospital – they will contact Dr Carmody. If there is no leak or bleeding within one hour after the procedure, you can resume life as normal. Paracetamol is helpful for mild uterine cramping.
A scan at the time of the problem is unnecessary. Generally, a scan in a day or two would be suggested, to see if the situation is settling.
The Fluorescent In-Situ Hybridization, or FISH test looks at the more common chromosome problems covering chromosomes 13 (Patau Syndrome) and 18 (Edward's Syndrome), 21 ( Down syndrome) and the sex chromosomes and is usually available within 24 hours on working days. These together account for over 90% of any bad chromosome results. Occasionally, there may not be enough skin cells in the amniotic fluid to perform both the FISH and the Final test. In this case, the laboratory will skip the FISH and proceed with the Final test which includes all chromosomes.
We will ring you with the results as they come in. A copy will be sent to your doctor. You will be contacted regardless of whether or not the FISH was successful. If a chromosome problem is detected, Dr Carmody will contact you with the result, and you will be given the opportunity to discuss the findings. You will be told what the abnormality is and how this will affect your baby. You will have the chance to discuss the results fully before making any decisions.