Hypoxic-Ischemic Encephalopathy (HIE) is a type of brain injury that can occur in newborns. The term “hypoxic” refers to a lack of oxygen, while “ischemic” indicates reduced blood flow. “Encephalopathy” broadly describes any condition causing brain dysfunction. HIE is a brain injury resulting from an insufficient supply of oxygen and blood to the brain, typically occurring around the time of birth. This interruption can permanently alter brain function, with its severity depending on the duration and extent of oxygen and blood deprivation.
Prevalence of HIE
The occurrence of Hypoxic-Ischemic Encephalopathy (HIE) varies considerably across the globe. Globally, HIE is estimated to affect between 1 and 6 out of every 1,000 live births, representing a significant concern for newborn health worldwide.
In high-income countries, the incidence of HIE is generally lower and has remained relatively stable. HIE occurs in approximately 1 to 3 per 1,000 live births, reflecting improvements in obstetric and newborn care that include better fetal monitoring and quicker interventions during difficult deliveries.
Low- and middle-income countries experience a much higher incidence of HIE. Estimates in these regions range from 2.3 to 30.6 cases per 1,000 live births. Some affected areas, like Sub-Saharan Africa, report HIE rates around 15 per 1,000 or more, nearly ten times higher than in wealthier nations. HIE, often called birth asphyxia, accounts for about 23% of global neonatal deaths. An estimated 1.2 million babies develop HIE globally each year, with 96% born in low- and middle-income countries.
Risk Factors Influencing HIE’s Incidence
HIE arises from events or conditions that disrupt the oxygen and blood supply to a baby’s brain. These factors can occur during pregnancy, throughout labor and delivery, or shortly after birth.
During pregnancy, several maternal and fetal health conditions can increase HIE risk. Maternal factors include very high or low blood pressure (such as preeclampsia or hypotension), infections (like chorioamnionitis), gestational diabetes, and substance use (such as drugs or alcohol). Fetal conditions, such as abnormal heart or lung development, fetal anemia, or intrauterine growth restriction, also pose a risk. Problems with the placenta, such as placental insufficiency, abruption (where the placenta separates too early), or previa (where the placenta covers the cervix), can severely limit the flow of oxygen and nutrients to the baby.
Complications during labor and delivery are frequent causes of HIE. Issues with the umbilical cord, such as cord prolapse (where the cord descends before the baby) or compression, can restrict oxygen flow. Uterine complications, including uterine rupture, present serious risks. Prolonged labor, a difficult delivery, or an abnormal fetal position can lead to fetal distress.
After birth, certain conditions can also cause HIE in a newborn. These include respiratory failure, severe infections like sepsis or meningitis, or very low blood pressure in the baby. Such events compromise the newborn’s ability to maintain adequate oxygen and blood supply to the brain, contributing to the overall incidence of HIE.
HIE in Diverse Populations
The commonness of HIE varies significantly across different groups and settings, providing a more detailed perspective on its prevalence. Factors such as gestational age, birth weight, and socioeconomic status influence how frequently this brain injury occurs. Understanding these variations highlights disparities in health outcomes.
Preterm infants, those born before 37 weeks of gestation, face a higher incidence of HIE compared to full-term infants. Some data suggest that HIE can occur in up to 60% of live births in preterm infants, or specifically, moderate to severe HIE at a rate of 37.3 per 1,000 babies born before 37 weeks. This contrasts sharply with the lower rates observed in full-term infants, which range from 3 to 20 per 1,000 live births. The developing brains of preterm infants are more fragile and thus more vulnerable to injuries that can lead to HIE.
Birth weight also plays a role in HIE incidence. Infants with low birth weight, particularly those weighing less than 2.5 kg, are at an increased risk. Conversely, infants with a high birth weight exceeding 4.0 kg can also have an elevated risk for moderate-to-severe HIE. These weight extremes suggest that deviations from a typical birth weight can predispose newborns to this condition.
Socioeconomic status and access to healthcare demonstrate profound differences in HIE commonness. Low- and middle-income countries consistently report much higher rates of HIE than high-income countries. This disparity is largely attributed to limited access to quality prenatal and perinatal care, often characterized by understaffed medical facilities and delayed interventions when a baby is in distress.
In these regions, a lack of adequate obstetric care, insufficient neonatal resuscitation practices, and limited access to therapeutic hypothermia contribute to the persistent burden of HIE. Even for babies with similar initial injury severity, socioeconomic vulnerability can influence their long-term outcomes. Infants from low socioeconomic backgrounds generally experience higher risks for various adverse health outcomes, including HIE. HIE remains a leading cause of both death and disability in low- and middle-income countries.