Neonatal hypoxic-ischemic encephalopathy (HIE) is a type of brain injury in newborn babies caused by a lack of oxygen and blood flow around the time of birth. It is a major threat to newborn health worldwide. In fact, HIE (often called “birth asphyxia”) accounts for about 23% of global neonatal deaths, and almost all of these deaths occur in low-resource settings. Each year an estimated 1.2 million babies develop HIE globally, with the vast majority (≈96%) born in low- and middle-income countries (LMICs).
Incidence refers to how often a condition occurs (typically given as cases per 1,000 live births for HIE). Over the past decade, the incidence of neonatal HIE has remained low and fairly stable in high-income countries (HIC). In places like the United States, Europe, Canada and Australia, HIE occurs in roughly 1 to 3 per 1,000 live births, and recent data from a U.S. cohort (2012–2019) showed a steady incidence around 1.7 per 1,000 births. This rate had dropped from higher levels in the early 2000s due to improvements in obstetric and newborn care (for example, better fetal monitoring and quicker interventions during difficult deliveries). By around 2015, the incidence in HICs had plateaued at a low level, indicating that while HIE still occurs, it is not increasing in frequency in these well-resourced settings.
In contrast, low- and middle-income countries continue to have a much higher incidence of HIE. Estimates vary across regions, but incidence in LMICs ranges roughly from 4 up to 26-30 cases per 1,000 live births. The worst-affected regions, such as parts of Sub-Saharan Africa, have HIE rates around 15 per 1,000 or more – nearly ten times higher than in wealthy countries. The higher incidence in LMICs is largely due to limited access to quality prenatal and perinatal care. Many births in these regions occur at home or in understaffed facilities, leading to delayed interventions when a baby is in distress. Over the last decade, global health efforts (like increasing hospital deliveries and training birth attendants) have started to slowly reduce the incidence of HIE in LMICs. However, progress is uneven, and HIE remains a common problem in poorer regions. Globally, the overall incidence of HIE has declined compared to past decades (dropping from an estimated ~11.7 per 1,000 in 1990 to ~8.5 per 1,000 in 2010), but since 2015 any further declines have been modest. The disparity between HICs and LMICs persists, with most HIE cases occurring in resource-limited countries.
Mortality is the rate of death caused by a condition. HIE is often fatal without proper care. Over the past ten years, mortality from HIE has significantly decreased in high-income countries thanks to advances in treatment, especially the widespread use of therapeutic hypothermia (cooling therapy). Therapeutic hypothermia, introduced in HICs around 2010, involves cooling the baby’s body to around 33°C for a few days to slow brain injury. This treatment has been proven to improve survival and reduce brain damage in moderate to severe HIE. Studies show that cooling can reduce the risk of death by about 10–20% compared to no cooling. For example, in the United Kingdom, HIE treatment improvements led to mortality among cooled infants dropping from about 13% in 2010 to 7% in 2017. Similarly, a national study in England/Wales observed that between 2011 and 2016, mortality in babies with moderate/severe HIE fell from ~17.5% to 12.3%. By the late 2010s, many HIC neonatal intensive care units (NICUs) report HIE mortality rates in the single digits (roughly 5–10% for moderate cases). This is a dramatic improvement compared to earlier eras when HIE mortality in HICs was much higher.
In LMICs, HIE still carries a much higher risk of death, although there have been slight improvements in some areas. Because most babies with HIE are born in settings with fewer resources, mortality remains a serious concern. Nearly 99% of all HIE-related newborn deaths occur in low-resource countries. In many LMIC hospitals that lack adequate technology and staff, HIE mortality rates can range from 20% up to 50% for moderate to severe cases. For instance, a recent clinical trial in South Asia (India, Sri Lanka, and Bangladesh) reported that about 31% of babies with moderate or severe HIE died even when given standard hospital care (without cooling). This means roughly one in three infants with serious HIE did not survive in that setting. Attempts to use cooling therapy in LMICs have faced challenges – a large 2021 study (the HELIX trial) found that cooling therapy in low-resource ICUs did not reduce HIE deaths and was associated with higher mortality, possibly due to lack of advanced supportive care. Over the 2015–2025 period, some LMICs have gradually improved basic newborn resuscitation and started a few cooling programs, which may have slightly lowered HIE mortality in certain hospitals. However, on the whole, HIE remains far deadlier in LMICs than in HICs. Hundreds of thousands of newborns still die each year from HIE in poorer countries, highlighting an urgent need for better perinatal care and appropriate interventions in those regions.
Morbidity refers to the long-term health problems or disabilities caused by a condition. Many infants who survive HIE do so with neurodevelopmental impairments. The severity of these impairments depends on how severe the HIE was and the quality of care received. Over the past decade, the outlook for HIE survivors in high-income countries has improved, although challenges remain. With prompt cooling therapy and modern neonatal intensive care, more infants are surviving with little to no disability after mild HIE, and even many moderate HIE survivors are doing better than before. Recent data from developed countries indicate a downward trend in serious disabilities among HIE survivors, thanks to better acute care and follow-up rehabilitation. For example, one population study in South Korea found that rates of cerebral palsy (a motor disability often caused by HIE) have significantly decreased in HIE children over recent years. Early intervention programs and therapies in HICs have also helped many HIE survivors achieve improved developmental outcomes.
Nevertheless, even in HICs, moderate and severe HIE can leave lasting effects. Common long-term morbidities include cerebral palsy, learning difficulties, epilepsy (seizure disorders), hearing loss, and vision problems. Studies estimate that roughly 1 in 3 children who suffer moderate-to-severe HIE develops cerebral palsy. Similarly, about 10–20% may develop epilepsy, and a significant number have some degree of learning or behavioral impairment. These outcomes have seen gradual improvement with time – the percentages used to be higher in the early 2000s, and they have been declining in HIC cohorts as medical care improves. Many children with mild HIE in HICs go on to have normal or near-normal development, though some may have subtle issues (for example, mild learning delays) that are only now being recognized in long-term studies.
In LMIC settings, the morbidity burden from HIE is often heavier. Babies who survive severe birth asphyxia in low-resource environments often do not have access to early interventions like physical therapy, occupational therapy, or special education services. As a result, a large proportion of HIE survivors in LMICs experience significant disabilities. For instance, without advanced care, 25–60% of infants who survive HIE may develop long-term neurological problems ranging from mild learning difficulties to severe cerebral palsy. Severe HIE in particular is very likely to cause profound impairment in survivors. The past decade has seen some growth of developmental follow-up programs in a few middle-income countries, which is a positive trend. However, generally speaking, the rate of serious neurodisability after HIE remains high in low-income regions, contributing to lifelong challenges for children and families and a sizable social burden.
Doctors classify HIE in newborns using Sarnat severity stages: mild (Stage I), moderate (Stage II), or severe (Stage III) HIE. The baby’s symptoms and neurological exam in the first days of life determine the stage. Outcomes vary greatly by these severity levels, and understanding this is important:
Over the decade from 2015 to 2025, we have seen important progress in the fight against neonatal HIE, and show declining mortality and morbidity from HIE in high-income countries, stable or slightly decreasing incidence globally, but ongoing high incidence and severe outcomes in low-income regions. In high-income countries, improved perinatal practices and advanced treatments (like therapeutic hypothermia) have stabilized HIE incidence at low levels and significantly reduced the risk of death or severe disability for affected babies. Parents in these countries can be cautiously optimistic that if HIE does occur, there is a strong chance the child will survive and lead a healthy life, especially in mild cases. Meanwhile, low- and middle-income countries have made some strides – for example, increasing hospital birth rates and training healthcare workers – which are slowly lowering the burden of HIE in some areas. However, the improvements are not yet enough. HIE remains one of the leading causes of newborn mortality and long-term disability in LMICs. The past decade’s trends highlight a clear need for greater global health investment in safe childbirth practices, emergency obstetric care, and affordable newborn therapies. Interventions must be adapted to low-resource settings (for instance, exploring simpler cooling methods or prevention strategies) to ensure that babies born in poorer regions have the same fighting chance as those in wealthier countries.
| HIE Severity | Setting | 2015 Baseline | 2025 Trend | Mortality | Long-term Disability |
|---|---|---|---|---|---|
| Mild HIE | HICs | Often not formally treated; thought to have excellent outcomes | Growing recognition of subtle challenges; more follow-up care | <1% | Low (~5–10%), some reports of learning/attention issues emerging in follow-ups |
| LMICs | Mild HIE often underdiagnosed or overlooked | Little change in awareness or intervention | Likely <1%, but data limited | Unknown, but disability may go undetected or unsupported | |
| Moderate HIE | HICs | Cooling therapy became standard of care; moderate disability risk | Continued improvement with early intervention and rehab | ~10–15% (↓ from ~20%) | ~30–50%, with better neurodevelopmental outcomes than in prior decades |
| LMICs | Limited access to NICUs, some cooling attempted | Variable care; outcomes still poor overall | ~25–35% | ~50–70%, often severe due to lack of follow-up services | |
| Severe HIE | HICs | High mortality and disability even with cooling | Modest mortality decline; disability still frequent and severe | ~35–45% (↓ from ~50–60%) | ~70–80%, some improvements in severity or quality of life |
| LMICs | High mortality and near-universal severe disability | No significant improvement; cooling often ineffective or harmful | ~40–60% | Very high, often >80%, with few supports for survivors |
What's Next?
High standards of care in HICs need to be maintained, and further quality improvement continued, and also invest in scalable, evidence-based neonatal interventions and developmental support systems in LMICs to close the outcome gap globally.
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