Chorionic villus sampling (CVS) is a type of prenatal testing. You may choose to undergo this genetic testing during pregnancy to check your unborn baby (fetus) for health conditions like Down syndrome. It also confirms sex.
CVS testing takes a small sample of cells from the placenta, the organ that forms during pregnancy to deliver nourishment to your baby.
The cells your healthcare provider removes are called chorionic villi. They’re formed from the fertilized egg, so they usually have the same genes as your baby.
Both CVS testing and amniocentesis are types of prenatal diagnostic testing. But providers perform them at different points during the pregnancy. CVS testing happens earlier in the pregnancy than amniocentesis. Typically, a CVS is performed at 10 to 13 weeks while amniocentesis is performed after 15 weeks gestation. In addition, there is some difference in what they test for. For example, amniocentesis can test for defects of the neural tube, the structure that turns into your baby's brain and spinal cord. Examples of these defects include spina bifida. CVS cannot detect these conditions.
Your healthcare provider can talk to you about your risk and recommend one of these tests, both of them or neither.
You undergo CVS testing when you’re 10 to 13 weeks pregnant.
CVS testing is not a standard part of prenatal care. Your healthcare provider may offer this option if you have certain risk factors, abnormalities detected on early ultrasounds or abnormal genetic (vs blood) screening. Having the test can detect genetic conditions during early pregnancy. But you can also choose to skip the test. It’s up to you.
Providers usually offer CVS testing if you:
. Already have a child with a known genetic condition.
. Are 35 or older on your due date, as the risk of having a baby with a genetic problem increases with the mother’s age.
. Had a previous screening or test that indicated a higher risk of having a child with a genetic condition. For example, noninvasive prenatal testing (NIPT), often done at 10 to 13 weeks, looks for the baby’s DNA in the mother’s blood.
. Have a family history of a genetic condition, or your partner does.
Your provider may recommend that you skip this testing if you:
. Have had vaginal bleeding during your pregnancy.
. Have an infection, such as an STI.
CVS can help identify certain genetic diseases, including problems with chromosomes. These cell structures hold the baby’s DNA. CVS can detect if there are extra or missing chromosomes or if any have significant changes to their structures. These types of chromosomal changes can lead to birth defects and other problems.
Conditions CVS tests for include:
. Down syndrome, or trisomy 21.
. Cystic fibrosis.
. Sickle cell disease.
. Tay-Sachs disease.
. Trisomy 18, or Edward syndrome.
CVS does not detect certain birth defects. For example, it can’t detect heart problems, cleft lip or palate or spina bifida. An ultrasound when you’re around 18 to 20 weeks pregnant checks for most birth defects.
If you have CVS, consider having a blood alpha-fetoprotein (AFP) test later in pregnancy. AFP screens for neural tube defects that CVS doesn’t detect.
There are several benefits of CVS testing:
. Accurate results: You can rely on CVS test results to make important healthcare decisions.
. Critical information: You may face a higher risk of having a baby with a genetic disorder or other problem. If so, you and your partner may want to know what’s going on with your baby as soon as possible. Having this information can help you make the best healthcare decisions. For example, you can prepare for special treatment your baby may need immediately after birth. Or you may decide not to continue the pregnancy.
. Earlier knowledge: You do CVS earlier in the pregnancy than amniocentesis. This helps you make choices at the beginning of the pregnancy. For example, the termination procedure is safer the sooner you do it.
Before the test, you have genetic counseling with either a certified genetic counselor or maternal-fetal medicine specialist. A genetic counselor discusses the risks and benefits of the procedure with you. You also have an ultrasound to confirm the gestational age (how many weeks pregnant you are). You want to do CVS testing at the right gestational age, when you’re between 10 to 13 weeks pregnant.
The risk of miscarriage for CVS and amniocentesis are about the same. The miscarriage risk with CVS is about 1 in 300-500.
Infection is another risk. And in rare cases, an infant may have limb deformity related to CVS testing. But most cases of limb deformity have happened when CVS was performed before the 10th week of pregnancy.
CVS testing is about 99% accurate. But CVS testing does not detect how severe the condition is.
The procedure does not hurt your baby.
Chorionic villus sampling is not painful, though you may feel some discomfort. There are two ways healthcare providers perform the test:
. Transcervical (through the vagina): Your provider inserts a speculum into your vagina. This smooth device is shaped like a duck’s bill and is also used for Pap tests. It allows your provider to widen the vaginal walls. Your provider then inserts a thin, plastic tube into your cervix. Guided by ultrasound, the provider moves the tube to the placenta and removes a small sample of villi.
. Transabdominal (through the abdomen, or belly): Again guided by ultrasound, your provider inserts a thin needle through your abdomen to the placenta to remove the cells. This process is like amniocentesis. If your provider uses the abdominal method, you may get local anesthesia to reduce any discomfort.
In the case of most twins, you may need a separate procedure for each baby. In rare cases, the provider may not have collected enough cells during the procedure. You may need a second one to get enough placental cells.
You may feel some cramping after the test. Some light vaginal spotting is normal. If your provider used a needle, you may also feel some soreness where they inserted it. You can typically go back to your regular activities the next day.
Your provider sends the sample of chorionic villi to a lab. Specialists in the lab grow the cells in a fluid and test them a few days later. You typically get some preliminary results within a few days. But certain rare conditions take longer to test for. You’ll get those results closer to 10 days to two weeks after the test.
Your genetic counselor contacts you with the results and discusses them with you. If the baby does have a genetic condition, you can talk with your counselor, partner and provider about how you’d like to proceed.
If cramping, soreness or bleeding don’t go away or get worse after CVS testing, contact your provider. You should also get in touch with your provider if you have:
. Amniotic fluid leaking, which may feel like urine leaking.