Chorionic Villus Sampling (CVS): A Comprehensive Guide

Chorionic Villus Sampling (CVS) is an early prenatal diagnostic test that analyzes placental tissue to detect genetic and chromosomal abnormalities. It supports early decision‑making, risk assessment, and comprehensive prenatal care in clinical practice.

Introduction

Prenatal diagnosis has revolutionised obstetric care by enabling the early detection of genetic and chromosomal conditions in the developing foetus. Among the various techniques available, Chorionic Villus Sampling (CVS) stands out as a pivotal invasive procedure, offering critical information to expecting parents and healthcare professionals.

History and Development of Chorionic Villus Sampling

The quest for early and accurate prenatal diagnosis began in the latter half of the twentieth century. Before the advent of CVS, amniocentesis was the primary method for obtaining foetal genetic material. However, it could only be performed after the 15th week of gestation, often delaying crucial decisions. In the late 1960s and early 1970s, researchers explored the possibility of sampling the chorionic villi—tiny projections from the placental tissue that share the foetus’s genetic makeup—for earlier diagnosis.

By the early 1980s, CVS emerged as a reliable method, allowing sampling as early as the 10th to 13th week of pregnancy. Over the decades, refinements in technique and imaging have enhanced its safety and diagnostic yield, cementing CVS as a mainstay in prenatal genetic evaluation.

What is Chorionic Villus Sampling?

Chorionic Villus Sampling is an invasive prenatal diagnostic procedure in which a small sample of chorionic villi is obtained from the placenta. The chorionic villi are finger-like projections containing foetal cells that originate from the same fertilised egg as the foetus itself. These cells harbour the complete genetic information of the developing baby, permitting detailed analysis for chromosomal abnormalities, single gene disorders, and other genetic conditions.

CVS can be performed via two main approaches: transcervical (through the cervix) and transabdominal (through the abdominal wall). The collected tissue is subjected to cytogenetic, molecular, and biochemical analyses, providing results earlier in gestation than most other invasive techniques.

Indications for CVS

CVS is primarily indicated when there is an increased risk of genetic or chromosomal disorders in the foetus. Some common scenarios include:

• Advanced maternal age: Women aged 35 years or older have a higher risk of having a child with chromosomal abnormalities such as Down syndrome.
• Abnormal findings in first trimester screening: When blood tests or ultrasound scans suggest a heightened risk of genetic conditions.
• Family history of genetic disorders: Parents with a history of chromosomal or single gene disorders may opt for CVS to detect the same in the foetus.
• Parental chromosomal rearrangements: Known balanced translocations or inversions in either parent may prompt targeted analysis.
• Previous child with genetic disorder: Couples who have previously given birth to a child with a genetic condition may seek reassurance or early diagnosis in subsequent pregnancies.
• Carrier status for specific genetic diseases: When both parents are carriers for autosomal recessive disorders such as thalassaemia, cystic fibrosis, or sickle cell anaemia.

Contraindications and Patient Selection

While CVS is invaluable in many scenarios, it is not suitable for every expectant mother. Contraindications and factors influencing patient selection include:

• Active vaginal or pelvic infection: Procedures can introduce infection to the uterus, risking maternal and foetal health.
• Vaginal bleeding or threatened miscarriage: CVS may exacerbate bleeding or increase the risk of pregnancy loss.
• Uterine anomalies: Structural abnormalities may make the procedure technically challenging or increase risks.
• Multiple pregnancies: CVS is technically more complex in twins or higher-order multiples, though not absolutely contraindicated.
• Maternal alloimmunisation: In certain immunological conditions, invasive procedures may increase risks to the foetus.
• Inability to access the placenta safely: Placental position or maternal factors may sometimes preclude safe sampling.

The CVS Procedure: Step-by-Step

The success and safety of CVS hinge on meticulous technique and experienced hands. The procedure is typically performed between the 10th and 13th week of gestation.

Pre-procedure Preparation

• Counselling and Informed Consent: The procedure, its risks, benefits, alternatives, and possible outcomes are explained. Written informed consent is obtained.
• Ultrasound Assessment: An ultrasound scan determines gestational age, foetal viability, placental location, and any anatomical considerations.
• Antiseptic Preparation: The abdominal or vaginal area is cleaned to minimise infection risk.

Transcervical CVS

1. The patient is placed in a lithotomy position, and a speculum is inserted to visualise the cervix.
2. Under continuous ultrasound guidance, a thin, flexible catheter is advanced through the cervical canal to the placental site.
3. Gentle suction is applied to aspirate a small sample of chorionic villi.
4. The catheter is withdrawn, and the sample is sent for laboratory analysis.

Transabdominal CVS

1. The patient lies supine, and the skin over the lower abdomen is cleaned and draped.
2. Using real-time ultrasound, the operator identifies the placental location and selects a safe entry point.
3. A local anaesthetic may be administered to numb the area.
4. A thin needle is inserted through the abdominal wall and uterus into the placenta.
5. Chorionic villi are aspirated using gentle suction.
6. The needle is withdrawn, and the sample is transported to the laboratory.

The entire procedure typically takes less than 30 minutes. Post-procedure, the patient is monitored for a short period for any immediate complications, such as bleeding or uterine contractions.

Risks and Complications

Like all invasive procedures, CVS carries certain risks, though advances in technique have brought complication rates down considerably. The major risks include:

• Miscarriage: The risk of miscarriage following CVS is estimated to be around 0.2% to 1%, slightly higher than amniocentesis when performed by experienced practitioners.
• Infection: There is a small risk of introducing infection into the uterus, which can lead to serious maternal and foetal complications.
• Bleeding and Cramping: Mild vaginal bleeding and uterine cramping are fairly common but usually self-limiting.
• Rh Sensitisation: In Rh-negative mothers, foetal blood cells may enter the maternal circulation, necessitating anti-D immunoglobulin administration to prevent isoimmunisation.
• Limb Abnormalities: Rarely, when performed before 10 weeks gestation, CVS has been associated with limb reduction defects.
• Sample Failure or Insufficient Tissue: Occasionally, the sample may be inadequate, necessitating repeat sampling or alternative testing.

To mitigate these risks, strict aseptic technique, ultrasound guidance, and adherence to recommended gestational age are essential. Patients are advised to rest post-procedure and report any severe pain, persistent bleeding, or fever.

Benefits and Limitations of CVS

CVS offers distinct advantages over other prenatal diagnostic methods, but it is not without limitations.

Benefits

• Early Diagnosis: CVS can be performed as early as 10 weeks, allowing for earlier detection and decision-making compared to amniocentesis, which is usually done after 15 weeks.
• Comprehensive Genetic Analysis: The sample allows for chromosomal, molecular, and some biochemical tests, enabling diagnosis of a broad spectrum of conditions.
• Rapid Results: Chromosomal analysis can be completed within a week, providing timely information.
• Enables Early Management Decisions: Results obtained early in pregnancy facilitate timely interventions, including continuation, preparation for a child with special needs, or, in some cases, consideration of pregnancy termination.

Limitations

• Cannot Detect All Conditions: CVS does not screen for neural tube defects like spina bifida, which require amniotic fluid analysis for alpha-fetoprotein (AFP).
• Confined Placental Mosaicism: In rare cases, the placenta may contain a mixture of normal and abnormal cells not representative of the foetus, complicating interpretation.
• Procedure-Related Risks: Although low, the risks of miscarriage, infection, and foetal injury cannot be entirely eliminated.
• Technical Failures: Inadequate sampling may necessitate repeat procedures or alternative testing.

Interpretation of Results

The tissue obtained via CVS undergoes a variety of analyses, depending on the indication:

• Karyotyping: Chromosomal analysis detects aneuploidies (e.g., trisomy 21, 18, 13), structural rearrangements, and large deletions or duplications.
• Fluorescence in situ Hybridisation (FISH): Provides rapid detection of common chromosomal abnormalities.
• Molecular Genetic Testing: PCR and DNA sequencing identify single gene disorders such as thalassaemia, sickle cell anaemia, and cystic fibrosis.
• Biochemical Analysis: In select cases, enzyme assays or metabolic studies are conducted for conditions like Tay-Sachs disease.

Most results are available within 7–14 days. It is important to note that CVS cannot detect all possible genetic or structural abnormalities. In cases of mosaicism, ambiguous results, or unexpected findings, further testing or genetic counselling may be necessary.

Comparison with Other Prenatal Diagnostic Techniques

Several prenatal diagnostic techniques are available, each with unique strengths and limitations. The main alternatives to CVS include amniocentesis and non-invasive prenatal testing (NIPT).

CVS vs. Amniocentesis

CVS vs. Non-Invasive Prenatal Testing (NIPT)

• NIPT analyses cell-free foetal DNA in maternal blood, offering high sensitivity and specificity for common aneuploidies without the risk of miscarriage.
• However, NIPT is a screening, not a diagnostic test. Positive results require confirmation by CVS or amniocentesis.
• NIPT cannot detect all genetic conditions, particularly single gene disorders or structural rearrangements, which CVS can diagnose.

Ethical and Psychological Considerations

Undergoing CVS is a significant decision for expectant parents, fraught with ethical and psychological implications. Comprehensive pre-procedure counselling is essential, covering:

• Informed Consent: Patients must understand the procedure, its risks, benefits, and alternatives.
• Implications of Results: The potential outcomes and their impact on pregnancy management should be discussed, including the possibility of difficult decisions regarding continuation or termination of pregnancy.
• Support Services: Genetic counselling, psychological support, and access to support groups are invaluable in helping families navigate the emotional landscape of prenatal diagnosis.
• Confidentiality: Respect for patient privacy and autonomy is paramount throughout the diagnostic process.

Healthcare professionals must approach CVS with sensitivity, acknowledging the anxiety and uncertainty that often accompany prenatal testing. A multidisciplinary approach involving obstetricians, geneticists, counsellors, and nursing staff ensures comprehensive care.

Nursing Care of Patients Undergoing Chorionic Villus Sampling

This test allows for early detection of various inherited diseases and chromosomal abnormalities, such as cystic fibrosis, sickle cell anemia, and Down syndrome. The role of the nurse is pivotal in providing care, education, and emotional support before, during, and after the procedure.

Pre-Procedure Nursing Care

Patient Assessment

• Medical History: Review the patient’s obstetric, medical, and genetic history. Assess for risk factors that may complicate the procedure, including bleeding disorders, infections, or allergies.
• Baseline Vital Signs: Record temperature, pulse, respiration, and blood pressure. These readings serve as a reference for post-procedural assessment.
• Laboratory Investigations: Confirm blood group, Rh status, and ensure completion of relevant blood tests, such as CBC and coagulation profile.
• Psychosocial Assessment: Evaluate the patient’s understanding of the procedure, expectations, anxieties, and support systems.

Patient Education and Preparation

• Informed Consent: Ensure the patient has received thorough counseling from the medical team about the risks, benefits, and alternatives. Witness and document the signing of the informed consent.
• Pre-Procedure Teaching: Explain the steps of CVS, including the technique (transcervical or transabdominal), the need for ultrasound guidance, and approximate duration.
• Discuss possible risks: miscarriage, bleeding, infection, and rare limb defects.
• Review pain management: Inform the patient that mild discomfort or cramping may occur.

Physical Preparation:

• Advise the patient to arrive with a moderately full bladder if a transabdominal approach is planned, to facilitate ultrasound imaging.
• Assist with appropriate clothing changes before the procedure.
• Ensure the availability of emergency equipment.

Supportive Measures:

• Encourage the presence of a supportive family member or companion.
• Answer questions and address any concerns empathetically.

Intra-Procedure Nursing Care

Assisting During CVS

• Maintaining Sterility: Prepare the procedure room with sterile instruments and supplies. Practice strict aseptic technique.
• Patient Positioning: Help the patient assume the required position (lithotomy for transcervical, supine for transabdominal).
• Vital Sign Monitoring: Continuously observe vital signs and record them at regular intervals.
• Emotional Support: Provide reassurance, maintain calm demeanor, and encourage slow, deep breathing if anxiety or pain arises.
• Assisting the Physician: Hand over instruments, adjust ultrasound equipment, and assist with specimen labeling and handling as per protocol.

Post-Procedure Nursing Care

Immediate Care

Observation:

• Monitor vital signs and fetal heart rate for at least one hour post-procedure.
• Assess for vaginal bleeding, leakage of amniotic fluid, abdominal pain, or uterine contractions.

Pain Management: Evaluate pain level and provide prescribed analgesics if needed.

Infection Prevention: Observe for signs of infection: fever, malaise, foul-smelling discharge. Instruct the patient to report these symptoms promptly.

Specimen Handling: Ensure proper labeling and immediate transport of the sample to the laboratory.

Patient Education After CVS

Activity Restrictions:

• Advise rest for the remainder of the day. Avoid strenuous physical activities, sexual intercourse, and heavy lifting for at least 48 hours.

Warning Signs:

• Educate the patient to seek immediate medical attention if experiencing excessive vaginal bleeding, severe abdominal pain, fever, chills, or passage of tissue.

Follow-Up:

• Schedule a follow-up visit within 1-2 weeks to review results and monitor maternal and fetal well-being.
• Arrange for additional support or counseling as needed, particularly if abnormal results are anticipated or received.

Psychosocial Support and Counseling

The emotional impact of CVS can be profound, especially as patients await diagnostic outcomes. Nurses play a crucial role in offering empathetic support and responsive counseling.

• Addressing Anxiety: Use active listening, validate the patient’s feelings, and offer relaxation techniques.
• Information Sharing: Provide updates regarding test progress and expected timelines for results.
• Family Involvement: Encourage family members to participate in discussions, supporting informed decision-making.
• Referral Services: Direct the patient to genetic counselors, social workers, or support groups if indicated.

Complications and Nursing Interventions

Though rare, complications may arise following CVS. Rapid recognition and intervention are essential.

• Hemorrhage: Immediately alert the healthcare provider, apply pressure if needed, and prepare for emergency management.
• Infection: Maintain strict aseptic technique, monitor for symptoms, and administer antibiotics if prescribed.
• Miscarriage: Provide emotional support, arrange for medical evaluation, and offer bereavement counseling if necessary.
• Rh Sensitization: For Rh-negative patients, ensure administration of Rh immunoglobulin following the procedure to prevent isoimmunization.

Documentation

Accurate and thorough documentation is imperative:

• Record: All patient assessments, vital signs, procedural details, specimen handling, and patient education provided.
• Report: Any adverse events, complications, or patient concerns promptly to the responsible physician.
• Maintain: Confidentiality and privacy in all records.

REFERENCES

1. Alfirevic Z, Navaratnam K, Mujezinovic F. Amniocentesis and chorionic villus sampling for prenatal diagnosis., https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6483702/. Cochrane Database Syst Rev. 2017;9(9):CD003252. Published 2017 Sep 4.
2. Maines J, Montero FJ. Chorionic Villus Sampling. [Updated 2025 Apr 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/sites/books/NBK563301/
3. American Pregnancy Association. Chorionic Villus Sampling: CVS. https://americanpregnancy.org/prenatal-testing/chorionic-villus-sampling/.
4. Gil MM, Molina FS, Rodríguez-Fernández M, et al. New approach for estimating risk of miscarriage after chorionic villus sampling. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7984173/. Ultrasound Obstet Gynecol. 2020;56(5):656-663.
5. Jones TM, Montero FJ. Chorionic Villus Sampling . https://www.ncbi.nlm.nih.gov/books/NBK563301/. 2022 Dec 11. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan.
6. March of Dimes (U.S.). Chorionic villus sampling. https://www.marchofdimes.org/find-support/topics/planning-baby/chorionic-villus-sampling). Last reviewed 1/2020.
7. National Health Service (UK). Chorionic Villus Sampling. https://www.nhs.uk/conditions/chorionic-villus-sampling-cvs/. Last reviewed 1/2023.
8. Pagana KD, Pagana TJ. Mosby’s Diagnostic and Laboratory Test Reference, 10th ed. Mosby: 2010.
9. Spinillo SL, Farina A, Sotiriadis A, et al. Pregnancy outcome of confined placental mosaicism: meta-analysis of cohort studies. https://pubmed.ncbi.nlm.nih.gov/35934121/. Am J Obstet Gynecol. 2022;227(5):714-727.e1.

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