Chorionic Villus Sampling (CVS) for Prenatal Testing: What to Expect
Doctors may recommend CVS for pregnant people who have an increased risk of chromosomal issues during their pregnancy.
The placenta is the organ that attaches to the uterus and develops around the fetus to provide nutrients, oxygen, immunity, and protection during pregnancy. During a CVS procedure, an OB-GYN or maternal-fetal medicine (MFM) specialist will take a tiny sample from the chorionic villi, the finger-like projections found on the placental tissue. The chorionic villi have the same genetic material as the fetus.
A CVS test can provide important information about chromosomal issues or congenital disabilities in a fetus. Using this information, parents can make decisions about the continuation of the pregnancy or make preparations for any special needs their baby may have.
Amniocentesis is another prenatal test that can detect genetic abnormalities in the fetus.
Rather than testing a sample of placental tissue, as CVS does, amniocentesis involves taking a sample of amniotic fluid from the placenta. Doctors insert a thin, long needle through the abdomen until it enters the uterus. The doctor will then extract a small volume of amniotic fluid for laboratory testing and evaluation.
Some key differences between CVS and amniocentesis include the following.
|Timing||10–13 weeks gestation||15–20 weeks gestation|
|Method||samples placental tissue||samples amniotic fluid|
|Procedure||can be performed abdominally or through the cervix||performed abdominally|
|Risk of miscarriage||1 in 455 procedures||1 in 900 procedures|
|Can test for||chromosomal conditions||chromosomal conditions, neural tube defects, Rh incompatibility, congenital anomalies|
While CVS carries a slightly higher risk than amniocentesis, being able to undergo the test sooner gives parents more time to make a decision about the pregnancy based on the results. If they choose to terminate the pregnancy, it is safer to do so earlier in gestation.
Though CVS testing is a prenatal test available to any pregnant person, it is not a standard part of prenatal care. This is because CVS presents a small risk of miscarriage.
Generally, OB-GYNs will only suggest CVS if the pregnant parent has risk factors, including:
- age over 35 for either parent, which increases the risk of chromosomal disorders
- genetic testing that indicates the birthing parent is a carrier for certain genetic diseases or disorders
- inconclusive or concerning results during previous tests, such as noninvasive prenatal testing, routine blood tests, or a nuchal translucency screening
- having a previous pregnancy or child with congenital anomalies
- family history of chromosomal disorders or congenital conditions
If you have any of these risk factors, your OB-GYN may recommend CVS testing. The test is optional, and the decision to undergo it is ultimately up to you.
Your doctor may also refer you to a genetic counselor, who can provide guidance on what a CVS test can detect, explain the results, talk about potential risks, and discuss your options with you.
CVS testing can detect chromosomal disorders, including:
- Down syndrome, also known as trisomy 21
- Edwards syndrome, also known as trisomy 18
- Patau syndrome, also known as trisomy 13
- Tay-Sachs disease, a fatal disease that causes fatty proteins to collect in the brain
- cystic fibrosis, a disease that causes mucus to build up in the lungs
- muscular dystrophy, a progressive disease that causes muscles to weaken and break down
- sickle cell disease, a condition that causes abnormally shaped red blood cells
chorionic villus sampling cannot detect
CVS testing cannot detect certain congenital conditions, including:
- neural tube defects, such as spina bifida
- congenital anomalies, such as cleft palate
- Rh incompatibility, when a birthing parent’s blood type is Rh-negative and the fetus’s blood type is Rh-positive, causing an immune reaction that attacks the fetus’s red blood cells
CVS testing is very accurate. However, although CVS can tell you if your fetus has a specific condition, it cannot indicate how severe the defect or disorder is.
OB-GYNs or MFM specialists can perform CVS from 10–13 weeks of pregnancy.
One of the advantages of CVS is that doctors can perform it in the first trimester. Having information earlier in your pregnancy can allow you to prepare and discuss your options with medical professionals. In some cases, it can help parents determine if they want to move forward with the pregnancy.
Your OB-GYN or genetic counselor can explain your options to you, considering your individual results and personal preferences.
Risk of miscarriage
- CVS: 1 in 455 procedures, or 0.22%, will result in a miscarriage.
- Amniocentesis: 1 in 900 procedures, or 0.11%, will result in a miscarriage.
Talk with your OB-GYN if you have concerns about your risk of pregnancy loss or miscarriage during CVS.
Other risks and complications
Other potential risks of CVS include:
- cramping and discomfort
- leaking of amniotic fluid or breaking of waters
- preterm labor
- limb defects in the fetus, rarely
An OB-GYN or MFM specialist performs CVS. You typically will undergo the procedure in an ultrasound suite within a clinician’s office.
There are two methods by which your doctor can collect placenta cell samples:
- Transcervical CVS: You will lie on your back while the doctor inserts a long thin tube through your cervix until it enters your uterus. Your doctor will use ultrasound imaging to ensure accuracy. The doctor will stop as the tube enters the space between the uterine lining and the fetal membrane, called the chorion. The doctor will then gather a sample of the chorionic villi through the tube using suction.
- Transabdominal CVS: Similarly, you will need to lie on your back. Your doctor will use ultrasound imaging to find the proper sampling placement. They will then insert a long, thin needle through your abdomen and uterine wall until it reaches the placenta. The doctor will then draw up a sample of the chorionic villi through the syringe.
Neither technique requires general anesthesia, though doctors may use a local anesthetic to numb the area. You may feel mild to moderate discomfort, similar to period cramping.
The overall procedure is relatively short. Collecting the sample takes minutes, and the full procedure takes around a half-hour.
After your test, your doctor will advise you to take it easy for at least 24 hours. Your doctor will also provide guidance on when it is safe to resume vigorous physical activity or sexual intercourse.
Your doctor will then send the sample to a laboratory for diagnostic testing. Results of a CVS test typically come back within 2 weeks. Your medical team or genetic counselor will review your results with you and provide guidance on options going forward.
CVS is a prenatal test that can diagnose certain chromosomal disorders in a fetus. Doctors can perform CVS from 10–13 weeks of pregnancy. This is earlier than amniocentesis, which doctors perform between weeks 15–20.
CVS testing carries a slightly higher risk of miscarriage than amniocentesis. However, the overall risk of miscarriage from CVS is very low, 0.22%.
Talk with your OB-GYN, maternal-fetal medicine specialist, or genetic counselor about the benefits and risks of CVS testing. They can also provide guidance on what the results could mean and the options available to you and your partner.