Most Common Causes of Neonatal Hypoxic-Ischemic Encephalopathy (HIE)
Hypoxic-ischemic injury is by far the most common cause of neonatal HIE, accounting for 46-65% of cases in both term and preterm infants. 1
Primary Etiologies of Neonatal HIE
Intrapartum Factors (Most Common)
- Placental insufficiency/infarction (strongest association with HIE, odds ratio 144) 2
- Placental abruption (odds ratio 101) 2
- Umbilical cord prolapse (odds ratio 74) 2
- Maternal anemia (odds ratio 26) 2
- Meconium-stained amniotic fluid (adjusted odds ratio 12.4) 3
- Prolonged second stage of labor (adjusted odds ratio 9.5) 3
- Acute sentinel events during labor (adjusted odds ratio 74.9) 3
- Abnormal fetal heart rate patterns (category 3 tracings are significantly more common in HIE cases) 3
Prematurity and Low Birth Weight
- Low birth weight is a major risk factor, with a 25% increase in HIE risk for every 500g reduction in birth weight 1
- Preterm infants have significantly higher incidence of HIE (affecting 22-30% of infants weighing less than 1kg) 1
Other Contributing Factors
- Perinatal ischemic stroke (10-12% of cases) 1
- Intracranial hemorrhage (10-12% of cases) 1
- Maternal factors: advanced age, multiple gestation pregnancy, placenta previa, preeclampsia 1
- Iatrogenic factors: use of fertility drugs or erythropoietin 1
- Delivery factors: breech presentation, being first-born 1
Epidemiology
- Overall prevalence of HIE remains relatively stable at approximately 1 per 1,000 live births 2
- Neonatal encephalopathy with hypoxemia occurs in about 32.8% of cases with birth asphyxia 1
- HIE is the most common cause of neonatal seizures, with approximately 90% of infants experiencing seizure onset within 2 days after birth 1
Clinical Implications
- HIE manifests as alterations in mental status, hypotonia, seizures, and abnormalities in feeding and respiration 4
- Therapeutic hypothermia is now standard of care for moderate to severe HIE, with treatment needed for 6-7 infants to prevent one death or disability 4
- Mortality rates associated with HIE have decreased from 11.5-12.3% (2010-2012) to 8.3-10.6% (2016-2018) 2
Diagnostic Considerations
- MRI with diffusion-weighted imaging is the most sensitive diagnostic tool for detecting HIE 1
- EEG monitoring is important for determining etiology and prognosis 4
- Cranial ultrasound alone identifies etiology in only about 38% of cases 1
Understanding these risk factors is crucial for early identification and intervention in cases of neonatal HIE, as prompt treatment with therapeutic hypothermia can significantly improve outcomes.