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Did Your Newborn Suffer Cerebral
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Incidence and Types of Hypoxic-Ischemic Encephalopathy


The incidence and epidemiology of hypoxic-ischemic encephalopathy (HIE) depend on whether a population-based approach or a hospital-based approach is used in the calculations. A hospital-based approach will reveal a higher incidence since they also serve as referral centers for high-risk pregnancies and other congenital conditions, which may be co-variables. Thus, a multi-factorial cause for HIE may alter the incidence.

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Likewise, rural and developing countries will likely experience higher rates of HIE due to inadequate facilities and technology during the birthing process. The second difficulty lies in the accuracy of diagnosis of HIE in comparison to other adverse cerebral events known as neonatal encephalopathy. Many of the retrospective studies included premature infants in their calculations, and the definition of HIE depends on including only near term or full term infants. The staging or classification system for the types of HIE was developed by Sarnat. But, the consistency of diagnosis and staging by type has not been well studied retrospectively.

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In one analysis in the United Kingdom, the incidence of HIE in the 1970's was 7.6 per 1000 live term births. In the 1980's, that number was 4.6 per 1000 term births, and in the 1990's, only 1.9 babies out of 1000 were born with the diagnosis of HIE. In the United States, The American College of Obstetricians and Gynecologists in conjunction with the American Academy of Pediatrics assess the overall incidence of HIE to range from 1.9 to 3.8 per 1000 live term births.

Types or Stages of HIE

The types of HIE are mild, moderate, and severe. Sarnat's criteria for classification are based on six parameters: alertness, activity level, muscle tone, reflexes, seizure activity, pupils and heart rate, and the duration of these signs. With mild or grade I form, full recovery is the norm. With moderate or grade II HIE, reflexes may also be slow or absent, but if the baby recovers within 1- 2 weeks, the long-term outcome is better. In severe or grade III cases, the severity and length of the seizures portend a worse prognosis. The modified Sarnat Staging System is without the EEG results. Those findings may impact the final diagnosis and prognosis.