Chorionic Villus Sampling for Prenatal Diagnosis:An In-depth Overview

Chorionic Villus Sampling (CVS) is an early prenatal diagnostic procedure that analyzes placental tissue to identify genetic and chromosomal abnormalities. It supports early detection, risk assessment, and informed decision‑making in prenatal care.

Introduction

Chorionic Villus Sampling (CVS) is a vital prenatal diagnostic procedure that has significantly advanced the field of obstetric medicine. It provides expectant parents and clinicians with early access to genetic and chromosomal information about the developing foetus, thereby enabling informed decision-making and early intervention when necessary. CVS is particularly relevant in the Indian context, where the prevalence of certain genetic disorders is higher due to consanguinity and other sociocultural factors.

Historical Perspective

CVS was first introduced in the late 1960s, with the primary aim of diagnosing genetic disorders in early pregnancy. The technique gradually gained popularity due to its ability to provide diagnostic information much earlier than amniocentesis, which is traditionally performed after 15 weeks of gestation. Over the decades, refinements in technique and improvements in ultrasound technology have enhanced the safety and accuracy of CVS, making it a standard option in modern prenatal care.

What is Chorionic Villus Sampling?

Chorionic Villus Sampling is an invasive prenatal diagnostic technique wherein a small sample of placental tissue (chorionic villi) is obtained for genetic analysis. The chorionic villi are finger-like projections that emerge from the chorion, one of the membranes surrounding the embryo. Since the genetic material in the chorionic villi is identical to that of the foetus, analysing these cells provides valuable information regarding the foetus’s chromosomal and genetic status.

Indications for Chorionic Villus Sampling

CVS is not a routine screening test but is specifically indicated for pregnancies at increased risk of genetic or chromosomal abnormalities. Common indications include:

• Advanced Maternal Age: Women aged 35 years or above at the expected date of delivery are at increased risk of chromosomal anomalies such as Down syndrome (Trisomy 21).
• Abnormal First-Trimester Screening Results: Elevated risk identified through combined first-trimester screening (nuchal translucency scan and biochemical markers).
• Family History of Genetic Disorders: Previous child with a chromosomal or genetic disorder, or parental carrier status for conditions such as thalassaemia, sickle cell anaemia, cystic fibrosis, or Duchenne muscular dystrophy.
• Parental Chromosomal Rearrangements: Balanced translocations, inversions, or other chromosomal abnormalities in either parent increase the risk of unbalanced chromosomal inheritance in the offspring.
• Positive Non-Invasive Prenatal Testing (NIPT): Abnormal cell-free foetal DNA results on maternal blood screening require confirmatory testing.
• Detection of Structural Abnormalities on Ultrasound: Major structural anomalies identified in the first trimester may warrant genetic evaluation.
• X-linked Disorders: Risk of passing on X-linked recessive disorders, such as haemophilia, especially when foetal sex determination is necessary for clinical management.

Timing of the Procedure

CVS is typically performed between 10 and 13 weeks of gestation. Performing the procedure before 10 weeks is generally avoided due to an increased risk of limb reduction defects and other complications. After 13 weeks, the benefits of early diagnosis diminish, and amniocentesis becomes the preferred diagnostic test.

Techniques of Chorionic Villus Sampling

There are two primary approaches to obtaining chorionic villus samples:

1. Transcervical CVS: A thin catheter is inserted through the cervix under ultrasound guidance to reach the placenta and aspirate a small amount of chorionic villi.
2. Transabdominal CVS: A fine needle is inserted through the abdominal wall and uterine muscle, guided by ultrasound, to access the placenta and withdraw chorionic villi.

The choice of technique depends on placental location, maternal anatomy, operator experience, and patient preference. Both methods have comparable success rates and complication profiles when performed by experienced practitioners.

Pre-procedure Preparation

Proper patient counselling and preparation are crucial for minimising anxiety and ensuring informed consent. Key steps include:

• Detailed History: Including previous obstetric history, family history of genetic disorders, and relevant medical conditions.
• Ultrasound Assessment: To confirm gestational age, placental location, number of foetuses, and viability.
• Counselling: Discussing the risks, benefits, alternatives, and limitations of CVS. Patients should be informed about possible complications, including miscarriage, infection, and ambiguous results.
• Informed Consent: Written consent is mandatory before proceeding with the procedure.

Procedure Details

The CVS procedure is generally performed as an outpatient procedure and does not typically require hospital admission.

Transcervical Approach:

1. The patient is placed in the lithotomy position.
2. The cervix is cleansed with an antiseptic solution.
3. Under continuous ultrasound guidance, a soft catheter is advanced through the cervical canal into the placenta.
4. Suction is applied to aspirate a small amount of chorionic villi.

Transabdominal Approach:

1. The patient lies in the supine position.
2. The abdomen is cleansed with an antiseptic solution.
3. Local anaesthesia may be applied at the puncture site.
4. Using ultrasound guidance, a fine needle is inserted through the abdominal wall into the placenta, avoiding the foetus and amniotic sac.
5. Chorionic villi are aspirated for analysis.

After the sample is obtained, it is immediately sent to the genetics laboratory for processing and analysis.

Laboratory Analysis

The chorionic villus sample can be subjected to various laboratory analyses, including:

• Karyotyping: Analysing the chromosomal complement of the foetus to detect aneuploidies (e.g., Trisomy 21, 18, 13) and structural chromosomal abnormalities.
• Molecular Genetic Testing: Targeted DNA analysis for specific single-gene disorders (e.g., thalassaemias, cystic fibrosis, sickle cell disease).
• Fluorescence In Situ Hybridisation (FISH): Rapid detection of common chromosomal abnormalities.
• Microarray Analysis: High-resolution detection of submicroscopic chromosomal imbalances (copy number variations).

Results from CVS are generally available within 7-14 days, depending on the complexity of the analysis.

Benefits of Chorionic Villus Sampling

CVS offers several advantages over other prenatal diagnostic procedures:

• Early Diagnosis: Allows detection of genetic or chromosomal disorders in the first trimester, enabling earlier decision-making regarding pregnancy continuation or termination.
• Comprehensive Genetic Information: Capable of detecting a wide range of chromosomal and single-gene disorders.
• Shorter Turnaround Time: Results are available earlier than with amniocentesis, allowing for timely interventions.
• Psychological Benefits: Early reassurance for low-risk cases and more time for counselling and decision-making for affected pregnancies.

Risks and Complications

While CVS is generally safe when performed by experienced practitioners, it is not entirely without risk. Potential complications include:

• Miscarriage: The most significant risk, with an estimated procedure-related risk of miscarriage ranging from 0.2% to 1%. The risk is slightly higher than that associated with second-trimester amniocentesis but has decreased with improved technique.
• Infection: Rare but can occur if aseptic technique is not strictly maintained.
• Bleeding and Cramping: Mild vaginal bleeding or abdominal cramps are relatively common and usually self-limiting.
• Foetal Limb Abnormalities: Early studies linked CVS before 10 weeks with limb reduction defects, but this risk is minimal when the procedure is performed after 10 weeks of gestation.
• Maternal Alloimmunisation: In Rh-negative mothers, anti-D immunoglobulin is given to prevent sensitisation.
• Confined Placental Mosaicism: Sometimes, chromosomal abnormalities are present in placental tissue but not in the foetus, or vice versa, leading to ambiguous or discordant results.
• Technical Failure: In rare cases, an adequate sample cannot be obtained, necessitating a repeat procedure or alternative testing.

Limitations of CVS

Despite its advantages, CVS has certain limitations:

• Cannot Detect All Birth Defects: Structural anomalies such as neural tube defects are not detected by CVS and require separate testing (e.g., maternal serum alpha-fetoprotein, targeted ultrasound).
• Confined Placental Mosaicism: As mentioned above, this can complicate interpretation of results and may require follow-up with amniocentesis.
• Limited to Known Genetic Disorders: Targeted molecular testing is only possible if the specific familial mutation is known.
• Risk of Ambiguous Results: Occasionally, results may be inconclusive, necessitating further investigations.

Comparison with Other Prenatal Diagnostic Techniques

Ethical and Social Considerations

The use of CVS for prenatal diagnosis raises several ethical and social issues, particularly in the Indian context where cultural, religious, and legal factors influence reproductive decision-making.

• Sex Selection: In some countries, prenatal sex determination is illegal under the Pre-Conception and Pre-Natal Diagnostic Techniques (PCPNDT) Act due to concerns about female foeticide. CVS must not be used for sex selection except for medically indicated reasons (such as X-linked disorders).
• Informed Consent: It is essential to ensure that patients understand the implications of the test results, including the possibility of ambiguous findings and the options available for pregnancy management.
• Psychological Impact: The emotional burden of making decisions based on prenatal diagnostic results can be significant, necessitating access to genetic counselling and psychological support.
• Confidentiality: The results of genetic testing should be kept confidential and shared only with authorised individuals.

Counselling and Support

Genetic counselling is an integral component of the CVS process. Counsellors provide information on the risks, benefits, and limitations of the procedure, as well as support in interpreting results and making informed decisions.

Clinical Implications and Recommendations

CVS remains a cornerstone of prenatal diagnosis for high-risk pregnancies. It enables early and accurate detection of chromosomal and genetic disorders, thereby improving pregnancy outcomes and enabling timely interventions. Clinicians must ensure that:

• Patients are appropriately selected based on risk factors.
• Comprehensive counselling is provided before and after the procedure.
• The procedure is performed by experienced practitioners using strict aseptic technique and ultrasound guidance.
• Results are interpreted in the context of clinical and family history, with follow-up testing as necessary.

Nursing Care for Patients Undergoing Chorionic Villus Sampling (CVS) Procedure

As an invasive procedure, CVS requires meticulous nursing care to ensure the safety, comfort, and psychological well-being of the patient.

Pre-Procedure Nursing Care

1. Patient Assessment

• Medical History: Review the patient’s obstetric, medical, and surgical history. Identify any potential contraindications, such as active vaginal bleeding, infections, or a history of miscarriage.
• Allergy Assessment: Check for allergies, particularly to latex or local anaesthetic agents.
• Vital Signs: Record baseline temperature, pulse, respiration, and blood pressure to compare with post-procedure readings.
• Gestational Age Confirmation: Confirm gestational age via ultrasound to ensure appropriateness for CVS (typically performed between 10 and 13 weeks of gestation).

2. Patient Education and Preparation

• Procedure Explanation: Clearly explain the purpose, steps, risks, benefits, and alternatives of the CVS procedure. Use simple, non-technical language and visual aids if necessary.
• Informed Consent: Ensure the patient (and partner, if present) understands the procedure and obtains written informed consent.
• Emotional Support: Address patient anxieties and fears. Provide reassurance and, if needed, refer to a counsellor or support group.
• Fasting Instructions: Inform the patient about any fasting requirements, though typically fasting is not required for CVS.
• Bladder Preparation: Depending on the approach (transabdominal or transcervical), instruct the patient to have a full or empty bladder as recommended by the physician.
• Pre-Procedure Investigations: Ensure completion of all necessary blood tests, including blood group and Rh typing, and screening for infectious diseases.

3. Environment and Equipment Preparation

• Privacy: Prepare a private, comfortable setting for the procedure.
• Equipment: Gather sterile equipment, including ultrasound machine, CVS needles, antiseptic solutions, sterile drapes, gloves, and specimen containers.
• Emergency Preparedness: Ensure availability of emergency equipment and medications in case of complications such as vasovagal reactions or allergic responses.

Intra-Procedure Nursing Care

1. Patient Support and Monitoring

• Positioning: Assist the patient into the appropriate position based on the chosen approach—supine for transabdominal, lithotomy for transcervical.
• Vital Signs Monitoring: Continuously monitor and record vital signs throughout the procedure to detect early signs of distress or complications.
• Assisting the Physician: Provide sterile equipment, maintain aseptic technique, and assist as directed during the procedure.
• Emotional Support: Offer reassurance, maintain eye contact, and encourage slow, deep breathing to reduce anxiety and discomfort.

2. Specimen Handling

• Labeling: Correctly label the specimen container with patient details, date, and time of collection to avoid identification errors.
• Transport: Ensure prompt and proper transport of the sample to the laboratory, following institutional protocols.

Post-Procedure Nursing Care

1. Immediate Post-Procedure Monitoring

• Vital Signs: Monitor the patient’s vital signs at regular intervals (e.g., every 15 minutes for the first hour) to detect early signs of complications such as bleeding or shock.
• Observation for Complications: Watch for signs of vaginal bleeding, amniotic fluid leakage, abdominal pain, uterine contractions, or infection. Report any abnormalities to the physician promptly.
• Rest and Comfort: Encourage the patient to rest in a comfortable position and provide analgesics as prescribed for pain relief.
• Emotional Reassurance: Provide continued support and answer any questions regarding the procedure and possible outcomes.

2. Patient Education Prior to Discharge

• Activity Restrictions: Advise the patient to avoid strenuous activities, heavy lifting, and sexual intercourse for at least 24-48 hours post-procedure or as directed by the physician.
• Signs of Complications: Educate the patient about symptoms that require immediate medical attention, such as:
  • Heavy vaginal bleeding
  • Severe abdominal pain or cramping
  • Fever or chills
  • Leakage of fluid from the vagina

• Follow-Up Appointments: Instruct the patient to attend all scheduled follow-up visits for ultrasound assessment and review of test results.
• Rh Immunoglobulin Administration: If the patient is Rh-negative, ensure administration of Rh immunoglobulin to prevent isoimmunization.

Psychological Considerations

Undergoing CVS can be a source of significant emotional stress and anxiety, given the implications of the results and the invasive nature of the procedure. Nurses play a vital role in providing psychological support by:

• Maintaining a calm and supportive demeanor
• Encouraging the patient to express concerns and fears
• Facilitating access to counselling services if needed
• Providing up-to-date information about the accuracy, limitations, and possible outcomes of CVS

Documentation

Accurate and thorough documentation is essential at every stage of the CVS procedure. Nurses should record:

• Assessment findings and baseline data
• Details of patient education and consent
• Time, route, and technique of the procedure
• Patient’s response during and after the procedure
• Any complications or interventions performed
• Instructions given at discharge

Special Considerations

• Cultural Sensitivity: Be aware of and respect cultural beliefs and practices that may influence the patient’s decision-making and experience with prenatal testing.
• Language Barriers: Use interpreters or translated materials as needed to ensure comprehension and informed consent.
• Partner Involvement: Encourage the presence and involvement of the partner or a support person for emotional comfort.

REFERENCES

1. American Academy of Family Physicians. Prenatal Diagnosis: Amniocentesis and CVS https://familydoctor.org/prenatal-diagnosis-amniocentesis-and-cvs/. Last updated 8/2022.
2. Young C, von Dadelszen P, Alfirevic Z. Instruments for chorionic villus sampling for prenatal diagnosis. Cochrane Database Syst Rev. 2013 Jan 31;2013(1):CD000114.
3. 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.
4. Alfirevic Z, Navaratnam K, Mujezinovic F. Amniocentesis and chorionic villus sampling for prenatal diagnosis. Cochrane Database Syst Rev. 2017 Sep 4;9(9):CD003252. doi: 10.1002/14651858.CD003252.pub2. PMID: 28869276; PMCID: PMC6483702.
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. 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.

Stories are the threads that bind us; through them, we understand each other, grow, and heal.

JOHN NOORD

Connect with “Nurses Lab Editorial Team”

I hope you found this information helpful. Do you have any questions or comments? Kindly write in comments section. Subscribe the Blog with your email so you can stay updated on upcoming events and the latest articles.