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Cordocentesis

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(Synonym: Percutaneous Umbilical Blood Sampling - PUBS)

1. DEFINITION

  • An invasive prenatal procedure allowing direct access to the fetal circulation by puncturing the umbilical cord under ultrasound guidance.
  • Purpose: To obtain fetal blood for analysis or to perform intrauterine transfusion.

2. TIMING

  • Gestational Age: Typically performed >18–20 weeks.
  • Rationale: Before 18 weeks, the umbilical cord is too thin and mobile, making the procedure technically difficult and risky.

3. INDICATIONS

With advancements in non-invasive monitoring (MCA Doppler) and molecular genetics (FISH on amniocytes), diagnostic indications have decreased.

A. Diagnostic Indications

  1. Fetal Anemia:
    • Gold standard for confirming fetal anemia in Rh Isoimmunization or Parvovirus B19 infection (indicated if MCA-PSV Doppler is >1.5 MoM).
  2. Rapid Karyotyping:
    • Used in late gestation (>24 weeks) when decisions must be made urgently (lymphocytes culture in 48–72 hours vs 10–14 days for amniocytes).
  3. Fetal Infection:
    • To detect IgM antibodies or viral load (e.g., CMV, Toxoplasmosis, Rubella) if amniocentesis is inconclusive.
  4. Hematological Disorders:
    • Fetal thrombocytopenia (NAIT - Alloimmune Thrombocytopenia).
    • Hemophilia / Coagulation profile.
  5. Assessment of Fetal Acid-Base Status:
    • In growth-restricted (IUGR) fetuses (rarely done now).

B. Therapeutic Indications

  1. Intrauterine Transfusion (IUT):
    • Transfusion of Packed Red Cells (for Hydrops Fetalis / Severe Anemia).
    • Platelet transfusion (for NAIT).
  2. Drug Administration:
    • Direct injection of drugs (e.g., Digoxin, Amiodarone) for fetal arrhythmias refractory to maternal therapy.

4. PROCEDURE

  1. Guidance: Continuous real-time high-resolution ultrasound.
  2. Target Site:
    • Preferred: Umbilical vein at the placental insertion site (cord root).
    • Reason: The cord is fixed at the insertion, minimizing movement during puncture.
    • Alternative: Free loop (technically harder).
  3. Technique:
    • 20–22 G spinal needle inserted transabdominally.
    • Fetal paralysis (Vecuronium) may be used to stop fetal movement.
  4. Verification:
    • Sample purity confirmed by Mean Corpuscular Volume (MCV) analysis (Fetal MCV is high >100 fL; Maternal is <100 fL) or Apt test (alkali denaturation).

5. COMPLICATIONS

Risk is higher than Amniocentesis or CVS.

  • Fetal Loss Rate: 1–2% (higher in hydropic fetuses).
  • Bradycardia: Transient fetal bradycardia is common (due to vasospasm).
  • Bleeding: Puncture site bleeding (usually transient; prolonged in thrombocytopenia).
  • Cord Hematoma: Can compress umbilical vessels leading to distress.
  • Fetomaternal Hemorrhage: Risk of worsening sensitization (Anti-D prophylaxis mandatory).

6. CONTRAINDICATIONS

  • Severe maternal oligohydramnios (difficult visualization).
  • Active maternal infection (e.g., HIV/Hepatitis - risk of vertical transmission).

7. CURRENT STATUS

  • Diagnostic use is declining because:
    • MCA-PSV Doppler (Middle Cerebral Artery Peak Systolic Velocity) is now the standard non-invasive screen for anemia.
    • FISH/PCR on amniotic fluid provides rapid genetic results without needing blood.
  • Currently, it is primarily a Therapeutic Procedure (for Transfusions).

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