Download the Consent for CVS
What is chorionic villus sampling?
Chorionic villus sampling (CVS) is a prenatal test that detects chromosomal abnormalities such as Down syndrome, as well as a host of other genetic disorders. The doctor takes cells from tiny fingerlike projections on the placenta called the chorionic villi and sends them to a lab for genetic analysis.
The main advantage of CVS over amniocentesis is that you can have it done earlier — generally between 11 and 13 weeks of pregnancy. (For an amniocentesis, you’ll have to wait until you’re at least 16 weeks pregnant.)
Women who choose to have CVS or amniocentesis are primarily those at increased risk for genetic and chromosomal problems. Because these tests are invasive, they carry a small risk of miscarriage.
What are the risks of CVS?
Although it’s often estimated to be between one in 75 and one in 100 — which is higher than the usual estimates for amniocentesis — there’s no real consensus on the actual risk of miscarriage due to CVS.
As with amniocentesis, the studies do not show consistent results and one center that does a lot of CVS recently found the miscarriage rate from the procedure was down to about 1 in 360 — similar to the center’s miscarriage rate from amniocentesis.
Because a certain percentage of women will end up miscarrying at this point in pregnancy anyway, there’s no way of knowing for sure whether a miscarriage following CVS was actually caused by the procedure. Your particular risk depends in large part on the skill and experience of the doctor performing the procedure.
There has been some concern that CVS is associated with limb defects in babies, such as missing fingers or toes, but this was primarily seen in tests done on women before 10 weeks of pregnancy. Current research suggests that there is no increased risk for this problem in women who have CVS at 11 weeks or later.
Is there any way to reduce the risks of CVS?
Ask your practitioner or genetic counselor to refer you to an experienced doctor who does a lot of CVS procedures and who is expert at both the transabdominal and transcervical procedures.
What is CVS like?
Before you have CVS, you’ll have an ultrasound to confirm how far along you are and to make sure it’s possible to get a good sample for the test.
The goal of CVS is to obtain a tiny tissue sample from your placenta, which will be sent to a lab for analysis. The doctor withdraws the sample through either your cervix or your abdomen, depending on which approach gives the best access to your placenta. A sonographer uses ultrasound to help guide the procedure.
If the doctor decides to go through your cervix, your vagina and cervix are first cleaned with an antiseptic. This is done to prevent any bacteria from entering the uterus, which could cause an infection. Under ultrasound guidance, the doctor then threads a catheter through the cervix and uses gentle suction to get a sample from the placenta.
If the CVS is going to be done through your abdomen, the doctor first numbs a spot on your abdomen with a shot of local anesthetic. A longer needle is inserted through your skin, muscle, and uterine wall to extract the sample.
Whether the tissue is obtained through your cervix or your abdomen, the amniotic sac where your baby is growing won’t be disturbed. When the test is done, we will check your baby’s heartbeat.
The procedure might hurt a little, but it’s over relatively quickly. It takes no longer than half an hour from start to finish and the extraction itself takes only a few minutes. Women who’ve had a transcervical CVS say it feels similar to a pap smear, which may feel like a cramp or pinch. Those who have a transabdominal CVS may experience some discomfort in the abdominal area.
Note: If your blood is Rh-negative, you’ll need a shot of Rh immunoglobulin after CVS (unless your baby’s father is Rh-negative as well) because your baby’s blood may have mixed with yours during the procedure and it may not be compatible.
What happens after the procedure?
You’ll need to take it easy for the rest of the day, so arrange for someone to drive you home. Avoid any heavy lifting, intercourse, and air travel for the next 24 hours.
You may have some minor cramping for a day or so. If you have significant cramping or vaginal spotting, or you’re leaking amniotic fluid, call your practitioner immediately. Also call right away if you have a fever, which could be a sign of an infection.
When will I get the results?
You should have the full results within two weeks. During this period, a technique called fluorescence in situ hybridization (FISH) may be used to look for select problems. Preliminary results of this test are available quickly, often in a couple of days.
What happens if my baby is found to have a problem?
You will be offered genetic counseling so that you can get more information and discuss your options. Some women opt to interrupt the pregnancy, while others decide to continue. Whichever route you choose, you may find that you want further counseling or support. Some women find support groups helpful, others may want individual counseling, and some may choose both. Be sure to let your nurse midwife, obstetrician, perinatologist, nurse, or sonographer know if you need more help so they can give you the appropriate referrals.