Chorionic Villus Sampling (CVS)

1. DEFINITION

An invasive prenatal diagnostic procedure involving the biopsy of placental tissue (trophoblasts) for genetic testing.

2. METHOD

A. Timing:

• Optimum: 10 – 13 weeks of gestation.
• Note: Not performed before 10 weeks due to risk of limb defects.

B. Approaches:

1. Transabdominal (Preferred): Needle inserted through the abdominal wall into the placenta (similar to amniocentesis). Safer and easier for fundal/anterior placentas.
2. Transcervical: Flexible catheter passed through the cervix. Used for posterior placentas but carries higher risk of infection and bleeding.

C. Procedure Steps:

1. Ultrasound Mapping: Confirm viability, gestational age, and placental location.
2. Asepsis: Cleaning of abdomen or vagina/cervix.
3. Sampling: Under continuous ultrasound guidance, the device (needle or catheter) is directed into the chorion frondosum (future placenta).
4. Aspiration: 15–20 mg of villi are aspirated using negative pressure.
5. Post-Procedure: Check fetal heart rate; Administer Anti-D Immunoglobulin if mother is Rh-negative.

3. INDICATIONS

Used when early diagnosis (First Trimester) is desired for termination or management.

A. Cytogenetic (Chromosomal)

• Abnormal First Trimester Screen (High NT, abnormal Dual marker).
• Advanced Maternal Age (>35 years).
• Previous child with chromosomal anomaly.
• Parental balanced translocation carrier.

B. Molecular (DNA Analysis)

• Single Gene Disorders: Ideally suited for families with known history of:
  • Thalassemia Major (Commonest indication in India).
  • Spinal Muscular Atrophy (SMA).
  • Duchenne Muscular Dystrophy (DMD).
  • Cystic Fibrosis.

C. Biochemical (Enzymatic)

• Inborn Errors of Metabolism detectable in trophoblasts (e.g., Tay-Sachs, Gaucher disease).

4. COMPLICATIONS

A. Fetal Risks

1. Fetal Loss (Miscarriage): Risk is 0.5 – 1.0% (comparable to amniocentesis in experienced centers, slightly higher in older data).
2. Limb Reduction Defects: Oro-mandibular limb hypogenesis syndrome is associated with CVS performed <10 weeks (due to vascular disruption).
3. Fetomaternal Hemorrhage: Risk of Rh isoimmunization.

B. Diagnostic Ambiguity

• Confined Placental Mosaicism (CPM): Occurs in 1–2% of samples. The placenta has abnormal cells, but the fetus is normal.
  • implication: Requires follow-up Amniocentesis to confirm.

C. Maternal Risks

• Vaginal Spotting/Bleeding: Common (~30% with transcervical route).
• Infection (Chorioamnionitis): Rare, but higher with transcervical approach.
• Leakage of fluid: Rare.