Chorionic Villus Sampling Test: Purpose, Test Details & Results

Chorionic Villus Sampling (CVS) is a pivotal test in modern prenatal care, offering early genetic insights and crucial decision-making support for expectant parents. With the advance of first-trimester screening, CVS has become an essential tool for detecting chromosomal, molecular, and biochemical disorders. This article explores the test’s purpose, details, and what to expect from the results, synthesizing findings from key medical studies and clinical experiences.

Purpose of Chorionic Villus Sampling Test

For many people, the journey of pregnancy is filled with anticipation and, sometimes, uncertainty. CVS is designed to provide early answers—especially for pregnancies at increased risk of genetic or chromosomal abnormalities. By analyzing placental tissue in the first trimester, CVS allows for earlier, more informed reproductive choices and medical care.

Early Genetic Diagnosis

CVS is primarily used for early detection of chromosomal abnormalities, most notably Down syndrome (trisomy 21), trisomy 18, and trisomy 13. Because it can be performed as early as 10 weeks into pregnancy, it enables decisions and interventions much sooner than amniocentesis, which is typically done at 16 weeks or later 2 3 6.

Candidates for the Test

CVS is commonly recommended for:

• Women aged 35 or older at delivery, due to elevated risk of chromosomal anomalies 6 12.
• Pregnancies with a family history of genetic disorders or previous child with a genetic condition 3 4.
• Detecting single-gene disorders using molecular techniques, such as cystic fibrosis, thalassemia, or hemoglobinopathies 4.
• Multiple gestations where each fetus can be individually assessed 5 8.

Additional Indications

CVS can also be indicated after abnormal first-trimester screening results (e.g., nuchal translucency or serum markers) or if parents are known carriers of certain genetic mutations 2 3 4. In rare cases, it may be used to assess fetal sex for X-linked diseases 4.

Chorionic Villus Sampling Test Details

Understanding how CVS is performed and what the process entails can help alleviate anxiety and ensure informed consent. The test involves collecting a small sample of placental tissue (chorionic villi) for laboratory analysis, using either a transcervical or transabdominal approach under ultrasound guidance.

Test Procedure: Step-by-Step

1. Pre-Test Preparation

• Ultrasound is performed to confirm gestational age, fetal viability, and placental location 6 10.
• Informed consent is obtained after counseling about risks, benefits, and alternatives 4.

2. Sampling Methods

There are two main routes for obtaining the sample:

• Transcervical: A thin tube or forceps is inserted through the cervix to reach the placenta 6 10.
• Transabdominal: A needle is passed through the abdomen into the uterus to access the placenta 10.

Both methods are guided by ultrasound imaging to ensure precision and minimize risks. The choice of approach depends on placental location, uterine anatomy, and operator preference 10.

3. Technical Considerations and Operator Skill

• Success rates are high for both methods (over 97%) when performed by skilled practitioners 10.
• Single-insertion success: Achieved in 90–94% of cases, reducing complications 10.
• Multiple insertion attempts increase the risk of complications, especially fetal loss 6.

4. Timing Matters

• Optimal timing: CVS is best performed between 10 and 14 weeks gestation 3 7.
• Risks with earlier sampling: Procedures before 10 weeks are linked with higher complication rates, including rare limb defects 3.
• Multiple gestations: Special care is taken to sample each fetus separately; high success rates have been documented 5 8.

Risks and Complications

• Fetal loss: The risk is slightly higher than amniocentesis, with most studies reporting a procedure-related loss rate of 0.6–1% above the background rate 6 7 9 10.
• Infection: Serious infections are very rare (≤0.08%) 6 9.
• Other complications: Minor risks include vaginal bleeding, cramping, or mosaic chromosomal results (where the sample shows mixed cell lines) 7 9 11.

Special Circumstances

• Failed sampling: Occurs in less than 1% of cases, often due to technical difficulties such as uterine fibroids 9.
• Need for further testing: In rare cases, ambiguous results or confined placental mosaicism may require follow-up amniocentesis 3 11 12.

Chorionic Villus Sampling Test Results & Follow-Up

Receiving CVS results is a pivotal moment for expectant parents. The results not only reveal crucial genetic information but also guide the next steps, whether it's reassurance, further testing, or difficult decision-making.

Types of Results

1. Chromosomal Analysis

• Karyotyping: Detects extra or missing chromosomes (e.g., trisomy 21) 3 6 11.
• Diagnostic accuracy: Over 99% when both direct and culture methods are used 6 9 11.
• False negatives: Extremely rare; most errors occur in cases of mosaicism or unusual aneuploidies 11 12.

2. Biochemical and Molecular Tests

• Single-gene disorders: DNA-based tests can identify mutations for conditions like cystic fibrosis, thalassemia, or sickle cell disease 3 4.
• Turnaround time: Results are often available within several days to two weeks, depending on the complexity of the test and laboratory workflow 3 6 11.

Interpreting Ambiguous Results

• Mosaicism: Sometimes, the placental sample contains a mix of normal and abnormal cells (confined placental mosaicism), which may not reflect the true fetal karyotype. In such cases, follow-up amniocentesis or fetal blood sampling may be recommended 3 7 11 12.
• Maternal cell contamination: Rare, but can sometimes lead to inaccurate results; laboratory protocols minimize this risk 11 12.

What Happens After the Results?

• Normal results: Offer reassurance and usually no further invasive testing is needed.
• Abnormal results: Genetic counseling is essential to discuss the diagnosis, implications, and reproductive options 3 4 12.
• Uncertain results: Additional testing, such as amniocentesis, may be recommended to clarify findings 3 11 12.
• Multiple gestations: Each fetus is reported separately; selective reduction may be considered in cases of severe abnormalities 5 8.

Follow-Up and Support

• Parents receive comprehensive counseling before and after the test to understand the results and consider next steps 4.
• Emotional support and, when needed, referral to specialists in genetics or fetal medicine are part of standard care 4 12.

Conclusion

Chorionic Villus Sampling is a cornerstone of modern prenatal testing, providing early, accurate, and actionable genetic information. While the decision to undergo CVS is deeply personal, understanding its purpose, procedure, and outcomes empowers parents and clinicians alike.

Key takeaways:

• Purpose: CVS enables early detection of chromosomal and genetic disorders, especially in high-risk pregnancies 2 3 6.
• Procedure: The test is performed between 10–14 weeks using transcervical or transabdominal approaches, with high success and low complication rates in skilled hands 6 7 9 10.
• Results: CVS offers rapid, reliable results for chromosomal, biochemical, and molecular analyses; ambiguous findings are rare but may require further testing 3 6 11 12.
• Follow-up: Genetic counseling and emotional support are integral to interpreting results and making informed choices 4 12.

Ultimately, CVS stands as a safe and effective option for early prenatal diagnosis, helping families navigate pregnancy with greater confidence and clarity.