Umbilical Cord Blood Gas Analysis: Comprehensive Interpretation and Clinical Outcomes 2025

Umbilical cord blood gas analysis provides valuable insights into fetal oxygenation and acid-base balance during labor and delivery. Proper interpretation of these values allows clinicians to assess the presence of hypoxia, acidosis, and the risk of long-term complications.

---

Key Components of Umbilical Cord Blood Gas Analysis

1. pH:

• Normal Values:
  • Umbilical artery: 7.18–7.38
  • Umbilical vein: 7.25–7.45
• Outcomes Based on pH:
  • pH
  • pH 7.0–7.1: Moderate risk for adverse neurodevelopmental outcomes.
  • pH >7.1: Generally associated with better outcomes.

1. Partial Pressure of Oxygen (pO₂):

• Normal Values:
  • Umbilical artery: 15–25 mmHg
  • Umbilical vein: 25–35 mmHg
• Clinical Significance of pO₂:
  • Low pO₂: Suggests hypoxemia due to poor placental oxygen transfer or umbilical cord compression.
  • A significant difference between arterial and venous pO₂ reflects proper oxygen extraction by fetal tissues.
• Outcomes Related to pO₂:
  • Persistent low pO₂ is linked to anaerobic metabolism, resulting in metabolic acidosis and organ dysfunction.

1. Partial Pressure of Carbon Dioxide (pCO₂):

• Normal Values:
  • Umbilical artery: 32–66 mmHg
  • Umbilical vein: 32–50 mmHg
• Elevated pCO₂ indicates respiratory acidosis, often a sign of acute hypoventilation.

1. Base Deficit/Excess (BD/BE):

• Normal Values:
  • Umbilical artery: (-8) to (+2) mmol/L
  • Umbilical vein: (-8) to (+2) mmol/L
• Clinical Significance of Base Deficit:
  • Mild Acidosis: Base deficit <8 mmol/L – Low risk of complications.
  • Moderate Acidosis: Base deficit 8–12 mmol/L – Requires close observation.
  • Severe Acidosis: Base deficit >12 mmol/L – Strongly associated with HIE and poor outcomes.

1. Bicarbonate (HCO₃⁻):

• Normal Values:
  • Umbilical artery: 16–24 mmol/L
  • Umbilical vein: 18–27 mmol/L
• Decreased levels indicate metabolic acidosis due to lactic acid accumulation.

---

Acid-Base Disturbances and Their Implications

1. Respiratory Acidosis:

• Findings: Low pH, high pCO₂, normal base deficit.
• Outcome: Typically resolves with adequate ventilation and rarely causes long-term effects if corrected quickly.

1. Metabolic Acidosis:

• Findings: Low pH, normal pCO₂, high base deficit.
• Outcome: Associated with prolonged hypoxia and increased risk of HIE, organ dysfunction, and developmental delays.

1. Mixed Acidosis:

• Findings: Low pH, high pCO₂, high base deficit.
• Outcome: Poor prognosis if not promptly managed, especially if pH 12 mmol/L.

---

Clinical Outcomes Related to pH, Base Deficit, and pO₂

1. pH 12 mmol/L:

• Strong predictor of HIE and poor neurodevelopmental outcomes.
• Immediate interventions, such as therapeutic hypothermia, are critical.

1. Low pO₂ and High Base Deficit:

• Reflects significant hypoxemia and anaerobic metabolism.
• These infants are at higher risk of multiorgan failure, requiring intensive monitoring in the NICU.

1. Arterial vs. Venous pO₂:

• The difference between arterial and venous pO₂ provides information about fetal oxygen utilization. A narrow difference may indicate insufficient oxygen delivery to tissues.

---

Management Based on Umbilical Blood Gas Analysis

1. Resuscitation:

• Initiate positive pressure ventilation for respiratory acidosis.
• Administer bicarbonate for severe metabolic acidosis (pH

1. NICU Admission:

• Monitor pH, pCO₂, and pO₂ to ensure improvement in oxygenation and acid-base status.
• Use therapeutic hypothermia for term or near-term infants with signs of encephalopathy.

1. Long-Term Monitoring:

• Babies with severe acidemia and hypoxemia should undergo regular neurodevelopmental evaluations.

---

Conclusion

Umbilical cord blood gas analysis, including pH, pO₂, pCO₂, and base deficit, is a crucial diagnostic tool in identifying perinatal hypoxia and its consequences. Proper interpretation guides neonatal resuscitation, NICU care, and long-term follow-up, ultimately improving outcomes for at-risk newborns.