What is Chorionic Villus Sampling (CVS)?
CVS is a test which takes a small sample of tissue, the chorionic villi, from your baby's placenta. The placenta almost always has the same genetic results as the baby. The placenta sample can be tested directly for chromosomal problems, like Down syndrome, or DNA abnormalities, like cystic fibrosis.
Who may be offered CVS?
A CVS is always voluntary and only you can decide if you should have this test. The information below may help you decide whether or not to have this test. The most common reason to have CVS is for those worried about the chances that the baby may have a chromosomal problem, like Down syndrome. This might include:
- Women with a First Trimester Screening (FTS) test suggesting an increased chance of having a baby with a chromosomal problem
- Women who are anxious about the risk of problems, often because of their age
- Women who have had a previous pregnancy affected by a serious medical problem with the baby
How is the CVS test performed?
CVS is performed in one of two ways, depending on the position of the placenta, as shown in the picture.
A fine needle is passed through the mother's abdomen and a sample from the placenta is taken. The needle is carefully directed to the right area using ultrasound.
Alternatively, a thin plastic straw is passed through the vagina and cervix into the placenta, similar in approach to a cervical smear. Ultrasound is also used to direct the straw to the right area.
When is the CVS test performed?
Ideally the test is performed between 11 to 12 weeks' gestation. However it may be performed as early as 10 weeks or as late as 14 weeks' gestation.
What preparation do I need before the test?
A moderately full bladder is preferable. This brings the pregnancy up into the abdominal cavity and therefore easier accessibility for the needle. A scan is first performed to make sure that the baby is alive and of the correct size, to check if there are twins, and to check the position of the placenta. It is possible that you may be asked to empty or re-fill your bladder in order to make sure that your uterus is in the best position.
It is important to know what your blood group is before the test. If possible please ask you doctor or midwife to provide this information to you, or bring along your blood donor card. If you have a negative blood group you will also need to have a special injection of "anti-D" after the CVS test.
What should I expect after the CVS procedure?
For the first couple of days after the procedure you may experience some abdominal cramping, like period pains, or a little bleeding from the vagina. These are relatively common and in the vast majority of cases are of no importance. You may find it helpful to take painkillers like paracetamol. If there is a lot of pain or bleeding or if you develop a temperature please seek medical advice immediately from your obstetrician or midwife or from the Irish Maternal Fetal Foundation.
When can I expect my results?
The results for Down syndrome and other major chromosomal problems are usually available within 2 weeks. However, if you wish to get your results sooner than this, you can choose to have a portion of the CVS sample sent to a special laboratory that can provide some results in 2 to 3 days. The results for other special genetic conditions may take 2 weeks or longer. We will call you with your results as soon as they are available. We will also send a copy to your obstetrician, GP or midwife.
Will the procedure need to be repeated?
In approximately 1% of cases an invasive test will need to be repeated because the test results are inconclusive, or if not enough placenta sample is obtained through the needle. In this situation you will have the option to undergo an amniocentesis test at about 15 weeks' gestation.
What are the risks associated with the test?
The risk of miscarriage due to CVS is about 1% (1 chance in 100). If a miscarriage is going to occur, you will usually have symptoms within the first 2 to 3 days after the test.fetal abnormalities. It is recommended that you have a Fetal Anomaly Scan at 20 weeks to check for other abnormalities.