What Is Chorionic Villus Sampling?

During your pregnancy, you’ll likely have several different tests and screening procedures at your disposal. One optional prenatal test is chorionic villus sampling (CVS), which can detect certain birth defects and genetic disorders in unborn babies.

“The CVS procedure involves taking a sample of chorionic villi cells, which are present on the outer membrane of the placenta, for testing,” says Nisarg Patel, MBBS, MS, a board-certified obstetrician and gynecologist. These cells have the same genes as the fetus.

Keep reading for everything you need to know about chorionic villus sampling, including why it’s performed, the benefits and risks, and more.
What Is Chorionic Villus Sampling (CVS)?
Chorionic villus sampling is a procedure that some people get between weeks 10 and 13 of pregnancy. It screens for certain chromosomal or genetic abnormalities in unborn babies.

Why Do People Get Chorionic Villus Sampling?
In some cases, the CVS test is performed as a follow-up to the noninvasive pregnancy testing (NIPT) that’s done sometime after the 10th week of pregnancy. NIPT tests for Down syndrome, trisomy 13, and trisomy 18, as well as other sex chromosome abnormalities.

If your NIPT results show an elevated risk of certain chromosomal abnormalities, your doctor may offer you a chorionic villus sampling test. This will allow them to get a better picture of whether something is wrong. CVS might also be recommended if your provider finds abnormalities on an early ultrasound.

Here’s a few other reasons why your doctor might recommend CVS during pregnancy.

Family history of genetic disease. If someone in your close family (or your partner’s family) has a genetic disease, your baby could have an elevated risk of having one as well.
Being 35 and older. If you’re 35 or older, your baby has a higher risk of genetic disorders—and being over 40 increases this risk even more.
Having an existing child with a genetic disorder. This increases your chances of having another baby with a genetic disorder.
What Does CVS Test For?
Chorionic villus sampling tests for the following conditions and more:

Down syndrome (trisomy 21)
Trisomy 18
Tay-Sachs disease
Cystic fibrosis
Sickle cell disease
Turner syndrome
When Is Chorionic Villus Sampling Done?
Not every person gets CVS during pregnancy. But if you’re recommended for the procedure because of certain risk factors, it’s performed between the 10th and 13th weeks of pregnancy.1 You’ll likely meet with a genetic counselor before CVS to understand the pros and cons.

What Does the CVS Procedure Look Like?
Before CVS, you’ll get an ultrasound to confirm your baby’s gestational age and position. The entire procedure takes about 30-45 minutes, though the extraction only lasts a few minutes, according to March of Dimes. It’s usually performed in your provider’s office or an outpatient facility.

There are two methods for performing the chorionic villus sampling test: transcervical and transabdominal.2 Your doctor will generally choose the test offering the simplest route to the placenta, according to the American Pregnancy Association. Here’s information about each type of CVS procedure.

Transcervical CVS: This type of CVS test involves inserting a catheter through the cervical opening into the uterus and taking samples from there.

Transabdominal CVS: In a transabdominal CVS procedure, your provider uses ultrasound imaging to guide a thin needle into the uterus through your abdomen, and they’ll take samples of cells from the placenta.
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Possible Risks of Chorionic Villus Sampling
The risks associated with CVS testing are low, but they do warrant a discussion with your doctor so that you fully understand them. Here are some possible complications associated with chorionic villus sampling:

Preterm labor
Rh sensitization (During CVS, a baby’s blood cells may enter the parent’s bloodstream, and this can cause complications if their blood types are different.)
Limb deformity in babies (This is rare and usually happens when CVS is performed too early—usually before 9 weeks, according to the Cleveland Clinic.)
Leaking amniotic fluid
Insufficient or inconclusive sampling
While these possible CVS complications may sound scary, rest assured the chances of them are low. Studies show that miscarriage rates associated with CVS range from 0.2% to 1%.3 Dr. Patel adds the risk of infection and Rh sensitization are also very low (less than 1% for each situation) and preterm labor is uncommon as well.

What Does CVS Feel Like?
Some people don’t feel anything during the CVS procedure, while others describe minor discomfort or cramping sensations, according to the March of Dimes.

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What to Expect After CVS Testing
After a CVS procedure, you’ll likely stay in the doctor’s office for around an hour to rest. “You may experience some mild cramping and discomfort afterwards, which usually lasts only a few minutes. You may also experience some light spotting or bleeding after the procedure,” says Dr. Patel. Your doctor may also suggest that you take a quiet break after CVS, as it can be emotionally draining.

Once the test is finished and your doctor feels comfortable with you leaving, you can go about your life. But you should rest and avoid strenuous activities for the first few days after CVS testing.

“If you experience any bleeding or spotting, contact your health care provider right away. It’s also a good idea to drink plenty of fluids and take acetaminophen (Tylenol) if needed for any cramping or pain, says Dr. Patel.

Dr. Patel advises also contacting your health care provider if you experience the following symptoms after CVS:

Heavy bleeding
Fluid leaking from the vagina
Fever or flu-like symptoms within 24 hours
CVS Procedure with Twins
If you’re having twins, you’ll might need two separate CVS procedures—one for each fetus.

Getting Results from Chorionic Villus Sampling
A lab will examine the material taken during CVS, and you’ll likely get results within 7 to 14 days. CVS testing results are about 99% accurate, according to the Cleveland Clinic, though it doesn’t detect the severity of conditions.

Most CVS tests detect no issues, but if the procedure uncovers a birth defect or genetic condition, your health care provider will guide you on the best course of action. Sometimes medication or surgery can correct the condition before delivery. Counseling with a genetics specialist might also be recommended, depending on the results. Either way, having knowledge of your baby’s condition can help you make informed decisions about continuing the pregnancy, and prepare for managing a child with special needs.

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Chorionic Villus Sampling vs. Amniocentesis
Amniocentesis is another prenatal diagnostic test, and it uses a small amount of amniotic fluid. Both CVS and amniocentesis are both more invasive than NIPT, but more accurate when it comes to detecting genetic abnormalities in your growing baby.

One main difference between CVS and amniocentesis is timing; the CVS procedure can be done earlier in pregnancy than amniocentesis (at 10-13 weeks compared to at least 15 weeks). This means CVS can give parents more time to make decisions or prepare themselves once they have the results.

Amniocentesis also tests for neural tube defects like spina bifida, which CVS doesn’t do.

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