Chorionic Villus Sampling (CVS): Complete Guide to Prenatal Genetic Testing

What Is Chorionic Villus Sampling?

Chorionic villus sampling (CVS) is a prenatal diagnostic procedure that collects a small sample of placental tissue called chorionic villi to test for chromosomal abnormalities and certain genetic disorders. The test can be performed from week 11 of pregnancy, providing earlier results than amniocentesis.

Chorionic villus sampling is one of the most important prenatal diagnostic tests available to expectant parents who want or need definitive genetic information about their developing baby. The procedure provides a high degree of accuracy in detecting various chromosomal conditions, including Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13), and sex chromosome abnormalities such as Turner syndrome and Klinefelter syndrome.

The chorionic villi are tiny finger-like projections of placental tissue that share the same genetic makeup as the developing fetus. Because the placenta develops from the same fertilized egg as the baby, analyzing the chromosomes in the chorionic villi provides accurate information about the baby's genetic composition. This makes CVS an invaluable tool for prenatal diagnosis.

Unlike screening tests such as first trimester combined screening (which includes nuchal translucency ultrasound and blood tests), CVS is a diagnostic test. This means it provides definitive answers rather than probability estimates. While screening tests can indicate whether there is an increased likelihood of a chromosomal abnormality, only diagnostic tests like CVS or amniocentesis can confirm or rule out these conditions with certainty.

The decision to undergo CVS is always voluntary. It is important that pregnant individuals and their partners receive comprehensive information about the procedure, its benefits, risks, and what the results might mean, so they can make an informed decision that aligns with their values and circumstances.

Why is the test called chorionic villus sampling?

The name comes from the biological structures being sampled. The chorion is the outermost membrane surrounding the developing embryo, which eventually develops into the placenta. The villi are the tiny, finger-like projections that extend from this membrane and are richly supplied with blood vessels. These villi are responsible for exchanging nutrients and waste products between the mother's bloodstream and the developing baby. By sampling these villi, doctors can obtain cells with the same genetic information as the baby.

What Conditions Can CVS Detect?

CVS can detect chromosomal abnormalities including Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13), sex chromosome abnormalities, and chromosomal structural changes. It can also detect certain inherited genetic diseases through DNA analysis, such as cystic fibrosis, hemophilia, and Huntington's disease.

The diagnostic capabilities of chorionic villus sampling are extensive and continue to expand as genetic testing technology advances. The analysis of chorionic villi can reveal important information about the baby's chromosomes and, in some cases, specific genes.

Every cell in the human body normally contains 46 chromosomes, arranged in 23 pairs. Half of these chromosomes come from the egg and half from the sperm. During the complex process of cell division that occurs after fertilization, errors can sometimes occur, leading to cells with an abnormal number of chromosomes or chromosomes with structural alterations. These chromosomal abnormalities can have significant effects on development and health.

Chromosomal abnormalities detected by CVS

The most common type of chromosomal abnormality is trisomy, where there is an extra copy of a chromosome. CVS can reliably detect several trisomies:

• Trisomy 21 (Down syndrome): The most common chromosomal abnormality, occurring in approximately 1 in 700 births. Individuals with Down syndrome have an extra copy of chromosome 21, which causes characteristic physical features and varying degrees of intellectual disability.
• Trisomy 18 (Edwards syndrome): A more severe condition occurring in approximately 1 in 5,000 births. Most affected pregnancies result in miscarriage, and those born with this condition typically have serious medical complications.
• Trisomy 13 (Patau syndrome): A rare and serious condition with multiple organ abnormalities, occurring in approximately 1 in 16,000 births.
• Sex chromosome abnormalities: Including Turner syndrome (45,X in females), Klinefelter syndrome (47,XXY in males), Triple X syndrome (47,XXX), and XYY syndrome.

In addition to detecting extra chromosomes, CVS can identify missing chromosomes (monosomies), larger structural changes in chromosomes (deletions, duplications, translocations), and other chromosomal rearrangements that might affect the baby's development.

Genetic diseases that can be tested through CVS

One significant advantage of CVS over amniocentesis is its ability to provide sufficient DNA for testing certain inherited genetic conditions. When there is a known family history of a genetic disorder, CVS can be used to determine whether the baby has inherited the disease-causing gene mutation. Conditions that can be tested through DNA analysis of CVS samples include:

• Cystic fibrosis: A condition affecting the lungs and digestive system
• Hemophilia: A blood clotting disorder
• Huntington's disease: A progressive neurological condition
• Sickle cell disease: A blood disorder affecting hemoglobin
• Tay-Sachs disease: A rare inherited metabolic disorder
• Muscular dystrophy: A group of muscle-wasting conditions

Who Should Consider Having CVS?

CVS may be recommended for pregnant individuals with increased probability of chromosomal abnormalities based on screening tests, those with a previous child with chromosomal abnormalities, known family history of genetic conditions, abnormal ultrasound findings, or advanced maternal age. The decision is always personal and voluntary.

While any pregnant person can technically request CVS, healthcare systems typically offer this invasive diagnostic test to those who have specific medical indications or risk factors. Understanding who might benefit most from CVS can help individuals and their healthcare providers make informed decisions about prenatal testing.

The primary reason for offering CVS is when there is an elevated probability that the baby may have a chromosomal abnormality or genetic condition. This probability can be established through various means, including screening tests, personal or family medical history, and ultrasound findings.

Common indications for CVS

Healthcare providers may offer or recommend CVS in the following circumstances:

• Abnormal first trimester screening results: If combined screening (nuchal translucency ultrasound plus blood tests for PAPP-A and beta-hCG) indicates an increased probability of chromosomal abnormality
• Abnormal NIPT results: Non-invasive prenatal testing (NIPT) may indicate increased risk, requiring confirmatory diagnostic testing
• Previous pregnancy affected by chromosomal abnormality: Having had a previous child with Down syndrome or another chromosomal condition increases the risk for future pregnancies
• Known chromosomal abnormality in parent: If either parent carries a chromosomal translocation or other rearrangement
• Family history of genetic disorders: When there is a known hereditary condition in the family that can be detected through CVS
• Abnormal ultrasound findings: Certain ultrasound findings may indicate increased risk of chromosomal problems
• Advanced maternal age: The risk of chromosomal abnormalities increases with maternal age, though age alone is less commonly used as an indication now that screening tests are widely available
• Parental request: Some parents prefer definitive diagnostic information regardless of their specific risk level

It is essential to remember that having one or more of these indications does not mean that the baby definitely has a chromosomal abnormality. Most pregnancies with increased screening risk still result in healthy babies. CVS provides a way to obtain definitive information, but the decision to undergo the procedure should be made after careful consideration of the benefits, risks, and personal circumstances.

How Is CVS Performed?

CVS is performed using a thin needle inserted through the abdomen (transabdominal approach) while using continuous ultrasound guidance. The procedure takes about 30 minutes total, with the actual sampling taking only a few minutes. Local anesthesia is optional as the needle prick is brief. Transcervical CVS through the cervix is also possible in some cases.

Understanding what happens during a CVS procedure can help reduce anxiety and enable better preparation. The procedure is typically performed by a maternal-fetal medicine specialist or a doctor with specialized training in invasive prenatal procedures. The entire appointment usually takes about 30 minutes, though the actual sampling process only takes a few minutes.

Preparation before the procedure

Before undergoing CVS, several preparatory steps are typically involved:

Your healthcare team will verify that you understand the procedure, including its purpose, benefits, and risks. You will be asked to provide informed consent. Blood tests are usually done beforehand to determine your Rh blood type, as Rh-negative individuals may need an injection of Rh immunoglobulin (anti-D) after the procedure to prevent Rh sensitization.

You may be asked to arrive with a comfortably full bladder, as this helps push the uterus into a better position for the procedure. However, this is not always necessary, and if you need to urinate before the procedure, it will not significantly affect the outcome. It can be helpful to have a support person accompany you to the appointment.

The transabdominal CVS procedure

The transabdominal approach is the most common method for CVS. Here is what to expect:

1. Ultrasound assessment: The procedure begins with a detailed ultrasound examination. The doctor will confirm the pregnancy dates, check the baby's position, and locate the placenta to determine the best approach for needle insertion. Gel is applied to your abdomen to enable clear ultrasound imaging.

2. Sterile preparation: The skin on your abdomen is cleaned with an antiseptic solution, and sterile drapes are placed around the area. This creates a clean field to minimize the risk of infection.

3. Needle insertion: Using continuous ultrasound guidance, the doctor inserts a thin needle through your abdominal wall, through the uterine wall, and into the placenta. The needle is guided to an area of chorionic villi that is safely away from the baby. Local anesthetic is optional; many women find the needle prick brief and tolerable without anesthesia.

4. Sample collection: Once the needle is correctly positioned, gentle suction is applied through the needle to aspirate a small sample of chorionic villi tissue. The doctor may need to make small adjustments to the needle position to collect an adequate sample. The sampling itself takes only about 1-2 minutes.

5. Post-procedure check: After the sample is collected, the needle is removed, and the doctor uses ultrasound to verify the baby's heartbeat and ensure everything looks normal. You may rest briefly before leaving.

Transcervical CVS

In some cases, particularly when the placenta is located on the back wall of the uterus, a transcervical approach may be used instead. In this method, a thin catheter or forceps is inserted through the vagina and cervix to reach the placenta. The choice between transabdominal and transcervical approaches depends on the placental position and the doctor's assessment of which method will be safest and most effective.

What Happens After CVS?

After CVS, rest for 24 hours and avoid heavy physical activity, sexual intercourse, and bathing. Mild cramping similar to menstrual pain is normal. Contact your healthcare provider if you experience heavy bleeding, fluid leakage, fever, or severe pain. Most people can resume normal activities after one day.

The immediate period after CVS is generally straightforward, but it is important to follow your healthcare provider's recommendations to support healing and minimize any risks. Understanding what is normal and what warrants medical attention will help you navigate the recovery period with confidence.

Immediate aftercare

Immediately after the procedure, you may rest for a short period at the clinic before going home. Your healthcare provider will give you specific instructions, which typically include:

• Rest at home for the remainder of the day
• Avoid strenuous physical activity and heavy lifting for 24 hours
• Avoid sexual intercourse for 24 hours (some providers recommend longer)
• Avoid bathing or swimming for 24 hours; showers are usually fine
• Stay well hydrated and eat normally

Most people can return to work and normal activities the day after the procedure, though some prefer to take it easy for a couple of days. Listen to your body and rest if you feel you need it.

Normal symptoms after CVS

It is common to experience some minor symptoms in the hours and days following CVS. Normal symptoms include:

• Mild cramping: Similar to menstrual cramps, this usually resolves within 24 hours
• Light spotting: A small amount of vaginal spotting is common and usually stops within a day or two
• Tender abdomen: The needle insertion site may feel slightly tender

These symptoms are generally mild and do not indicate any problem with the pregnancy. Over-the-counter pain relievers such as acetaminophen (paracetamol) can help with cramping, but avoid aspirin and ibuprofen unless your doctor advises otherwise.

How Long Does It Take to Get CVS Results?

Preliminary CVS results for the most common chromosomal abnormalities (trisomy 21, 18, 13) are often available within 2-3 days using rapid testing methods. Complete chromosomal analysis takes about 1-2 weeks. DNA analysis for specific genetic conditions may take 2-3 weeks. Normal results are typically communicated by letter; abnormal results are discussed directly with you.

The waiting period for CVS results can be an anxious time for expectant parents. Understanding the timeline and what the different types of results mean can help manage expectations and prepare for the next steps.

Types of analysis and timing

The chorionic villi sample undergoes laboratory analysis that can include several types of testing:

Rapid results (2-3 days): Many laboratories offer rapid testing methods, such as quantitative fluorescent polymerase chain reaction (QF-PCR) or fluorescence in situ hybridization (FISH), which can detect the most common chromosomal abnormalities within 2-3 working days. These tests specifically look for trisomy 21 (Down syndrome), trisomy 18, trisomy 13, and sex chromosome abnormalities.

Full karyotype (1-2 weeks): A complete chromosomal analysis, called karyotyping, requires the cells from the chorionic villi sample to be cultured in the laboratory. This process takes longer but provides a comprehensive picture of all 46 chromosomes, including the detection of less common chromosomal abnormalities and structural changes. Results are typically available within 10-14 days.

DNA analysis (2-3 weeks): If specific genetic conditions are being tested through DNA analysis, results may take 2-3 weeks depending on the complexity of the testing involved.

Receiving your results

The way results are communicated varies between healthcare centers. Commonly, if results are normal, you may receive a letter or phone call. If abnormal results are found, a healthcare provider will typically contact you directly to arrange a consultation where the results can be explained in detail and appropriate support and information can be provided.

If you have not received results within the expected timeframe, do not hesitate to contact your healthcare provider. Occasionally, laboratory issues may require a repeat sample, though this is uncommon.

Understanding your results

In approximately 99% of cases, CVS provides a clear result that definitively indicates whether the tested chromosomal abnormalities are present or absent. However, in about 1% of cases, a finding called confined placental mosaicism may occur. This is when some cells in the placenta have a chromosomal abnormality while the baby's cells are normal (or vice versa). If this occurs, you may be offered amniocentesis to clarify the baby's actual chromosomal status.

What Are the Risks of CVS?

The main risk of CVS is procedure-related miscarriage, which occurs in fewer than 1 in 200 procedures (less than 0.5%) when performed by experienced specialists. Other rare risks include infection, amniotic fluid leakage, and Rh sensitization (preventable with anti-D injection). The risk of limb abnormalities is only associated with CVS performed before week 10, which is why the procedure is not done before week 11.

Like any invasive medical procedure, CVS carries certain risks. It is important to understand these risks in order to make an informed decision about whether to proceed with the test. The good news is that serious complications are uncommon, especially when the procedure is performed by experienced practitioners at specialized centers.

Miscarriage risk

The most significant risk associated with CVS is procedure-related miscarriage. Modern research shows that the additional miscarriage risk attributable to the CVS procedure itself is less than 0.5%, or fewer than 1 in 200 procedures, when performed by experienced operators. This figure has improved considerably over the years as techniques and ultrasound guidance have advanced.

It is important to note that the background miscarriage rate in early pregnancy (before any invasive testing) is approximately 2-3% at the gestational age when CVS is typically performed. This means that some miscarriages after CVS would have occurred regardless of the procedure. The additional risk from the procedure itself is small when placed in this context.

The miscarriage risk is highest in the first two weeks after the procedure. After this time, the risk returns to the baseline for your pregnancy.

Other potential risks

• Infection: Very rare (less than 1 in 1,000 procedures) due to sterile techniques used during the procedure
• Amniotic fluid leakage: Uncommon, and if it occurs, usually resolves on its own
• Rh sensitization: Can occur if Rh-negative blood mixes with Rh-positive fetal cells; prevented by giving Rh immunoglobulin (anti-D injection) after the procedure
• Need for repeat procedure: In approximately 1-2% of cases, an inadequate sample may require a repeat CVS or alternative testing

Historical concerns about limb abnormalities

In the early days of CVS, when the procedure was sometimes performed before week 10 of pregnancy, there were reports of an increased risk of limb abnormalities in babies. This is why CVS is now only performed from week 11 onwards. When performed at or after 11 weeks of gestation, there is no evidence of increased risk of limb abnormalities.

Making the Decision About Prenatal Testing

The decision to have CVS is entirely personal and voluntary. Consider what you would do with the information, discuss with your partner and healthcare provider, and take time to think through your options. Whatever you decide is the right decision for your family. Genetic counseling is available to help you understand your options and make an informed choice.

Deciding whether to undergo CVS can be one of the more challenging decisions of pregnancy. There is no universally "right" answer - the best decision depends on your individual circumstances, values, beliefs, and what information would be helpful for your pregnancy and family planning.

Before making a decision, it can be helpful to reflect on several questions: What would you do with the information if an abnormality were detected? Would knowing in advance help you prepare emotionally, practically, or medically? How would you feel about the small risk of miscarriage associated with the procedure? Would uncertainty about the baby's health be more stressful than the risks of testing?

For some families, having definitive information allows them to prepare for a child with special needs, access support services, and make informed decisions about the pregnancy. For others, the information would not change their decisions, making the small risks of the procedure seem unnecessary. Both perspectives are valid.

Support for your decision

Genetic counseling is an important resource available to help you navigate the decision-making process. Genetic counselors are healthcare professionals trained to provide information about genetic conditions, testing options, and the implications of different results. They offer non-directive counseling, meaning they support whatever decision you make without trying to influence you in a particular direction.

If you are a partner or co-parent, it can be valuable to discuss the decision together, though ultimately the pregnant person has the right to make the final decision about any medical procedure involving their body. Healthcare providers should support the autonomous choice of the pregnant individual.

What Are the Alternatives to CVS?

Alternatives to CVS include amniocentesis (performed from week 15-16 with similar accuracy), non-invasive prenatal testing (NIPT - a blood test with high accuracy for common trisomies), and first trimester combined screening. Detailed ultrasound can also provide information about fetal anatomy, though it cannot diagnose chromosomal conditions with certainty.

If you are considering prenatal genetic testing, it is helpful to understand all the options available so you can choose the approach that best fits your situation and preferences.

Amniocentesis

Amniocentesis is another invasive diagnostic test that, like CVS, can definitively detect chromosomal abnormalities. It is performed from week 15-16 of pregnancy by inserting a thin needle through the abdomen to collect a sample of amniotic fluid. The accuracy for detecting chromosomal abnormalities is comparable to CVS (over 99%). The main differences are timing (later than CVS) and the sample type (amniotic fluid vs. placental tissue). Amniocentesis may be preferred if CVS is not available or not technically feasible due to placental position.

Non-invasive prenatal testing (NIPT)

NIPT is a screening test (not a diagnostic test) that analyzes cell-free fetal DNA circulating in the pregnant person's blood. It has high sensitivity and specificity for detecting trisomy 21, 18, and 13, typically greater than 99% for Down syndrome. However, because it is a screening test, positive results should be confirmed with a diagnostic test such as CVS or amniocentesis. NIPT can be performed from week 10 of pregnancy and carries no risk of miscarriage.

First trimester combined screening

This screening approach combines nuchal translucency ultrasound measurement (the fluid at the back of the baby's neck) with blood tests measuring PAPP-A and beta-hCG. The results give a probability estimate for the most common chromosomal abnormalities. This screening has a detection rate of approximately 85-90% for Down syndrome. It is typically performed between weeks 11 and 14.

Detailed ultrasound

Ultrasound examinations throughout pregnancy can detect many physical abnormalities and some markers associated with chromosomal conditions. However, ultrasound alone cannot diagnose chromosomal abnormalities with certainty. A detailed anomaly scan, typically performed around week 18-20, provides comprehensive assessment of fetal anatomy.