Chorionic Villus Sampling (CVS) for Prenatal Testing: What to Expect

Medically Reviewed By Valinda Riggins Nwadike, MD, MPH
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Chorionic villus sampling (CVS) is a prenatal diagnostic test that uses a sample of placental tissue to gather genetic information about a fetus. CVS can test for certain chromosomal disorders and congenital disabilities with high accuracy sooner than other forms of prenatal testing.

What is chorionic villus sampling?

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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.

CVS carries a small risk of miscarriage, slightly higher than the risk associated with amniocentesis. Doctors can perform a CVS test as early as 10 weeks of pregnancy.

How is chorionic villus sampling different from amniocentesis?

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.

CVSAmniocentesis
Timing10–13 weeks gestation15–20 weeks gestation
Methodsamples placental tissuesamples amniotic fluid
Procedurecan be performed abdominally or through the cervixperformed abdominally
Risk of miscarriage1 in 455 procedures1 in 900 procedures
Can test forchromosomal conditionschromosomal 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.

Learn about other medical tests you may undergo during pregnancy.

What are the reasons for a chorionic villus sampling test?

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.

Learn more about reasons for genetic testing.

What does a chorionic villus sampling test detect?

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

What

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.  

Learn more about common hereditary diseases.

When is chorionic villus sampling performed?

OB-GYNs or MFM specialists can perform CVS from 10–13 weeks of pregnancy.

What are the advantages and risks of chorionic villus sampling?

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 is a safe procedure, and the overall risk of pregnancy loss is very low. However, the risk is about twice as high for CVS as for amniocentesis.

  • 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
  • bleeding 
  • leaking of amniotic fluid or breaking of waters
  • infection
  • preterm labor
  • limb defects in the fetus, rarely

What should I expect during a chorionic villus sampling procedure?

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.

Summary

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.

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Medical Reviewer: Valinda Riggins Nwadike, MD, MPH
Last Review Date: 2022 May 19
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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