Cordocentesis

(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).