How is birth asphyxia classified?

Classification of Birth Asphyxia

Birth asphyxia is classified based on severity using multiple integrated criteria including umbilical artery pH, Apgar scores, presence of organ dysfunction, and clinical encephalopathy—not by Apgar score alone, which has poor sensitivity and specificity. 1

Severity Classification System

Birth asphyxia severity is stratified into three categories based on umbilical artery base deficit and clinical complications 2:

• Mild asphyxia: Umbilical artery base deficit >12 mmol/L without significant organ dysfunction 2
• Moderate asphyxia: Umbilical artery base deficit >12 mmol/L with neonatal encephalopathy or single organ system complications 2
• Severe asphyxia: Umbilical artery base deficit >12 mmol/L with multi-organ dysfunction (three or more organs) and/or hypoxic-ischemic encephalopathy 1

Diagnostic Criteria (Multi-Index Approach)

The diagnosis requires all of the following four criteria to be met 1:

1. Low Apgar scores with respiratory depression present (sensitivity 100%, specificity 98.90%) 1

2. Umbilical artery blood pH <7.00 (sensitivity 44.44%, specificity 96.05%) 1

   • If pH is only <7.20, all other criteria must be present 1
   • Severe fetal acidemia (pH <7.00) indicates increased risk of adverse neurologic sequelae 3

3. Hypoxic-ischemic organ injury with at least one organ dysfunction (sensitivity 100%, specificity 96.62%) 1

   • Common affected organs include brain, kidneys, heart, liver, and intestines 4

4. Exclusion of other causes of low Apgar scores through differential diagnosis 1

   • Must rule out congenital heart disease, inborn errors of metabolism, prematurity complications, and maternal medication effects 4

Antepartum high-risk factors serve as reference (sensitivity 100%, specificity 17.99%) but are not diagnostic alone 1

Clinical Assessment Components

Apgar Score Limitations

• Apgar scores alone have <50% sensitivity for diagnosing severe birth asphyxia 5
• Normal Apgar scores do not exclude severe birth asphyxia 5
• Only 50.9% of low Apgar score cases actually represent true asphyxia 1
• Respiratory depression must be present for diagnostic validity 1

Optimal Timing for Assessment

Arterial pH and base deficit at 30 minutes of life are the best criteria for diagnosing severe birth asphyxia 5, though they lack positive predictive value 5

Neurological Prognostic Scoring

A single neurological score at 30 minutes of life based on consciousness, respiration, and neonatal reflexes provides the best short-term neurological prognosis 5

Pathophysiologic Context

Birth asphyxia represents severe disturbance of oxygen supply during labor, confirmed by 6:

• Severe metabolic acidosis in umbilical cord blood
• Persistent low Apgar scores
• Functional disturbances from hypoxic damage in multiple organs including the central nervous system

The fetus responds to asphyxia by redistributing cardiac output to protect vital organs (brain, myocardium, adrenal glands) at the expense of decreased flow to kidneys and intestines 3

Critical Pitfalls to Avoid

• Never diagnose asphyxia based solely on Apgar scores—this leads to significant misdiagnosis 1
• Do not assume all low Apgar scores represent asphyxia—differential diagnosis is mandatory 1
• Recognize that umbilical artery pH <7.20 alone is insufficient without supporting clinical criteria 1
• Distinguish true intrapartum asphyxia from antepartum brain damage that may produce similar symptoms 6