Chorionic Villi - Understanding Chorionic Villus Sampling

These Placental Projections Contain Your Baby's Genetic Makeup

Doctor and pregnant woman looking at digital tablet
Hero Images/Getty Images

Chorionic villi are finger-like projections on the edge of the placenta that faces the uterine wall. The prenatal test known as chorionic villus sampling (CVS) involves taking a sample from the chorionic villi to analyze the developing baby's DNA.

The Role of the Placenta and Chorionic Villi

The placenta is the physical link between your and your developing baby. When you become pregnant, the placenta is the organ inside your uterus that supports your fetus' growth and development by providing oxygen, nutrients and hormones and taking away waste such as carbon dioxide through the umbilical cord.

Chorionic villi are tiny projections on the placenta where much of this exchange occurs. They have the same genetic makeup as your fetus, so they can be used for genetic testing.

What Is Chorionic Villus Sampling?

Chorionic villus sampling is a type of prenatal test. It's a highly accurate genetic test that can be done when your fetus is 10 to 12 weeks old. It can tell you if your baby will have genetic abnormalities that cause conditions such as Down syndrome or Tay-Sachs disease

CVS can be done earlier in your pregnancy than the other common fetal diagnostic test, amniocentesis. However, unlike amniocentesis, it cannot tell you if your developing baby has a neural tube defect. 

Who Gets CVS?

Chorionic villus sampling is not recommended for every woman, in part because there are health risks. Up to 1 in 100 women who have CVS will have a miscarriage.

Your doctor may suggest you have CVS if:

  • You are 35 or older.
  • You have had past pregnancies with genetic problems.
  • You or your partner has a family history of genetic disorders.

How Chorionic Villus Sampling Works

A sample of chorionic villi can be taken one of two ways: 

  • Transcervical procedure - a thin plastic tube called a catheter is guided through your vagina and cervix to reach the placenta. 
  • Transabdominal procedure - a needle is inserted through your abdomen and uterus to reach the placenta.

​In both cases, your doctor will use an ultrasound to safely find the chorionic villi and obtain the sample. 

What to Expect - During and after Chorionic Villus Sampling

For some women, CVS is painless. Some women have cramping (like period cramps) during the sampling. Women who have a transcervical procedure often compare it to getting a Pap smear

Getting the sample takes about five minutes, although including the set up the test can take 30 to 45 minutes.

After the test, you should spend the day resting. Some women have spotting or cramping for a few hours. If you have more serious symptoms - heavy bleeding, fever or contractions - call your doctor right away. 

The results of your CVS will come back within two weeks, often earlier. The results of genetic testing can help you decide if you want to continue the pregnancy or how to prepare for your baby. 

Also Known As: chorionic villus (singular)

Common Misspellings: choronic villi, chronic villi

Sources:

Frequently Asked Questions: Prenatal Development: How Your Baby Grows During Pregnancy. American Congress of Obstetricians and Gynecologists. June 2015.

Chorionic Villus Sampling. MedlinePlus. U.S. National Library of Medicine. November 16, 2014.

Chorionic villus sampling. March of Dimes. August 2011.

Gude, N.M., Roberts, C.T., Kalionis, B. (2004). Growth and function of the normal human placenta. Thrombosis Research.

Continue Reading