Prenatal Test – Chorionic villus sampling (CVS)
Chorionic villus sampling (or CVS) is a prenatal test that is performed between weeks 10 to 12 of your pregnancy. It is used to detect chromosomal abnormalities, such as Down syndrome. This test is done by analyzing the genetic makeup of cells taken from the chorionic villi, which are finger like projections on the placenta. CVS is 99% accurate in detecting hundreds of chromosomal defects. If you are determined to be at risk for these defects your doctor or midwife may recommend you have CVS.
The CVS test is done by removing a small sample of the placenta from the uterus. The sample is removed with a needle or a thin tube called a catheter. The sample will either be taken through the cervix or by inserting a needle into the abdomen. First an ultrasound will be done to verify the age of the fetus. The ultrasound will be used to determine the position of the placenta and to guide the needle or catheter. Depending on where your placenta is, the chorionic villi cells will be removed through your cervix (transcervical CVS), which is more common, or through the abdomen (transabdominal CVS). For the transcervical CVS your vagina and cervix will be cleaned with an antiseptic to prevent infection. A catheter will be threaded through the cervix and suction will be used to get the sample. For a transabdominal CVS the doctor will numb a spot on your abdomen with a local anesthetic. Then a needle will be inserted into your abdomen to extract the sample. When complete, the doctor may listen to the baby’s heartbeat to make sure that the baby is doing well. You’ll want to rest for the rest of the day after your test and usually you’ll be advised to avoid strenuous activity, including sex and exercise for about three days.
Most women feel fine after the test, but may experience some mild spotting. The procedure itself can hurt a little, but only takes about 30 minutes from start to finish. The actual removal of tissue only takes a few moments. The transcervical CVS is less uncomfortable than the transabdomial CVS procedure. There is a small chance of miscarriage for this test. Additionally, some studies suggest that CVS may cause defects in the infant’s fingers or toes if done too early.