What chorionic villus sampling is and what it shows

Chorionic villus sampling (CVS) is a prenatal test that examines genetic material from the placenta to check for certain chromosomal conditions and genetic disorders. A doctor takes a small tissue sample from the placenta—either through the cervix or through the abdomen—and sends it to a lab for analysis. The test can detect Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13), and some single-gene disorders like cystic fibrosis or sickle cell disease, depending on what the test is designed to look for.

CVS is typically performed between 10 and 13 weeks of pregnancy. Unlike some other prenatal screening tests that estimate risk, CVS gives a direct answer about whether the chromosomal condition is present. This is why it is called a diagnostic test rather than a screening test. The results usually come back within one to two weeks, though some labs may take longer.

Key Takeaways

  • CVS directly detects chromosomal conditions like Down syndrome and some genetic disorders by analyzing placental tissue, rather than estimating risk like screening tests do.
  • The test is performed between 10 and 13 weeks of pregnancy through either a cervical or abdominal approach, depending on placenta position and other factors.
  • CVS carries a small risk of miscarriage—roughly 1 in 200 to 1 in 400 depending on the provider and technique—which is why it is typically offered to people with higher-risk pregnancies.
  • Results usually arrive within one to two weeks and show whether a condition is present, not whether it will cause symptoms or how severe it might be.
  • Some pregnancies produce unclear results that require follow-up testing, and a small percentage of samples fail and must be repeated.

When CVS is typically offered

CVS is not routine for all pregnancies. It is usually offered when earlier screening tests—such as first-trimester combined screening or cell-free DNA screening—show a higher risk of chromosomal conditions, or when a person has a family history of a genetic disorder. It may also be recommended if a previous pregnancy was affected by a chromosomal condition, if a parent carries a balanced chromosomal rearrangement, or if ultrasound findings raise concern.

Some people choose CVS earlier in pregnancy than other diagnostic tests because it can be done in the first trimester, which gives more time to process results and make decisions. Others choose it because they want a definitive answer rather than a probability. Your doctor or genetic counselor can discuss whether CVS makes sense for your specific situation.

How the procedure works

CVS is performed by an obstetrician or maternal-fetal medicine specialist, usually in a hospital or specialized clinic. The procedure takes about 10 to 15 minutes. The doctor uses ultrasound to locate the placenta and guide the sampling instrument. There are two approaches: transcervical CVS, where a thin catheter passes through the cervix to reach the placenta, and transabdominal CVS, where a needle passes through the abdomen and uterine wall to the placenta. The choice depends on where the placenta is positioned and other individual factors.

During the procedure, you remain awake and can watch the ultrasound screen. You may feel pressure or mild cramping, but the procedure itself is not typically painful. Some spotting or light cramping afterward is normal. You can usually return to normal activity the same day, though your doctor may recommend resting for the remainder of that day.

What the results mean

A normal CVS result means the chromosomal condition being tested for was not detected. An abnormal result means the condition is present. However, a positive result for a chromosomal condition does not predict how severely it will affect the person or what their quality of life will be. Two people with Down syndrome, for example, may have very different abilities and health needs. The test shows presence or absence, not severity or prognosis.

Some results are unclear or inconclusive. This can happen if the sample contains maternal cells mixed with placental cells, if there is mosaicism (some cells have the condition and others do not), or if the lab cannot grow enough cells to analyze. In these cases, you may need follow-up testing, such as amniocentesis later in pregnancy or additional ultrasound imaging. A small percentage of samples fail to produce results and must be repeated.

Risks and limitations of CVS

The main risk of CVS is miscarriage. The risk varies by provider, technique, and individual factors, but is generally reported as roughly 1 in 200 to 1 in 400. This is higher than the miscarriage risk from amniocentesis (roughly 1 in 300 to 1 in 500), which is why CVS is not offered to everyone—only to those for whom the information is important enough to justify the risk. Your doctor should discuss this risk with you before the procedure.

Other possible complications are rare but include infection, leaking amniotic fluid, or vaginal bleeding or spotting. CVS cannot detect neural tube defects like spina bifida, so if there is concern about these conditions, additional screening such as measurement of alpha-fetoprotein (AFP) may be recommended. CVS also does not screen for all genetic conditions—only those specifically tested for, which is why your doctor will discuss what the test can and cannot detect.

CVS compared to other prenatal testing options

Several prenatal tests exist, and they work in different ways. First-trimester combined screening (nuchal translucency ultrasound plus blood tests) and cell-free DNA screening (also called noninvasive prenatal testing or NIPT) estimate the risk of chromosomal conditions but do not diagnose them. They are screening tests, not diagnostic tests. Amniocentesis, performed between 15 and 20 weeks, is another diagnostic test that samples amniotic fluid instead of placental tissue and carries a similar but slightly lower miscarriage risk than CVS.

The choice between these tests depends on timing, risk tolerance, and what information matters most to you. Some people do screening first to see if risk is high enough to warrant a diagnostic test. Others skip screening and go straight to a diagnostic test if they want a definitive answer early. Genetic counseling can help you understand the differences and think through which approach fits your values and circumstances.

What to expect before and after the procedure

Before CVS, you will have an ultrasound to confirm pregnancy dating, check fetal development, and determine placenta position. Your doctor will review your medical history and discuss the risks and benefits. You may meet with a genetic counselor who can explain what the test can show and help you think about what you would do with different results. This conversation is important—it helps may support you are making a choice that aligns with your own values, not just following a recommendation.

After the procedure, rest for the remainder of the day if possible. Contact your doctor if you experience heavy vaginal bleeding, severe cramping, fever, or leaking fluid. You will receive results by phone or at a follow-up appointment. If results are abnormal or unclear, your doctor will discuss next steps, which may include genetic counseling, additional testing, or referral to a specialist. Having support—whether from a partner, family member, counselor, or support group—can be helpful while you process results and make decisions.

Frequently Asked Questions

Is CVS safe for the baby?

CVS is generally safe, but it does carry a small risk of miscarriage—roughly 1 in 200 to 1 in 400. Serious complications like infection or injury to the fetus are very rare. Your doctor can discuss your individual risk based on your pregnancy and medical history.

Can CVS detect all genetic conditions?

No. CVS detects chromosomal conditions like Down syndrome and some single-gene disorders if the test is specifically designed to look for them. It does not detect neural tube defects, and it does not screen for all possible genetic conditions. Your doctor will explain what the specific test can and cannot show.

What if I get an abnormal result—do I have to do anything?

An abnormal result does not require you to do anything. Some people choose to continue the pregnancy, some choose to end it, and some use the information to prepare for birth or plan medical care. Genetic counseling and support from your healthcare team can help you think through your options.

How long does it take to get results?

Most labs return CVS results within one to two weeks. Some labs are faster; others may take longer. Ask your doctor for a timeline specific to the lab they use. If results are unclear, follow-up testing may add additional time.

Can I do CVS if I have had a previous miscarriage?

Yes, but your doctor will review your history and discuss whether the procedure is right for you. A previous miscarriage does not automatically mean you cannot have CVS, but it may affect the risk assessment and the decision about whether to proceed.