Hypoxic-Ischemic Encephalopathy Risk Factors and Related Conditions
Risk factors and related conditions for a term infant developing Hypoxic-Ischemic Encephalopathy (HIE) are associated with socioeconomic factors, pre-pregnancy and peri-partum events, existing medical conditions of the mother and the baby, genetic and intrinsic birth defects, and acquired medical conditions or illnesses of pregnancy. The birth prevalence of moderate to severe HIE was 3.8 per 1000 live term births according to one study. There were 9.1% neonatal fatalities in that same study. Overall newborn encephalopathy is heterogenous with multiple factors and interacting causes which makes analysis of the risk factors difficult.
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In evaluating the results, the diagnosis of moderate to severe HIE, grades II -III was made based on the presence of seizures or any two of the following findings that lasted longer than 24 hours: abnormal consciousness, abnormal tone and reflexes, breathing maintenance difficulties, or feeding problems.
Socioeconomic Findings
Despite being correlated positively, advanced maternal age increased the risk of birthing a baby with HIE while having an increased number of successful live births decreased the risk for developing HIE. Lack of private insurance and unemployment increased the chance of birthing a child who developed HIE.
Medical Conditions
Infertility that required treatment increased the number of couples conceiving and thus was associated with a 4-fold increase risk of developing HIE. The infertility treatment itself, other inherent predispositions, and maternal age could independently contribute to HIE. A family history of recurrent seizures or other neurologic conditions might be factors as well. Thyroid disorders were also correlated with the increased risk of HIE in the infant.
Maternal Conditions During the Pregnancy
Severe preeclampsia is a risk factor for HIE. This could be due to placental insufficiency or chronic placental abruption which is when the placenta pulls away from the uterine wall and bleeding ensues. Any moderate or severe bleeding during pregnancy from any cause including abruption or abnormal placement of the placenta can diminish the blood flow and oxygen to the fetus. Viral infections such as rubella, cytomegalavirus, and Zika might contribute as can elevated maternal temperatures. The inflammatory response may be a factor in these cases. Cigarette smoking had no effect on HIE, but this could be due to the increased risk of prematurity in these patients and the diagnosis of HIE requires a term infant. Alcohol intake actually was shown to lower the risk of HIE. The reasons are unknown, but the uterine relaxing effects of alcohol are well established since intravenous alcohol was once a treatment for premature labor.
Infant Conditions
Post term infants, those 42 weeks and beyond were at increased risk of HIE and this was believed to be related to diminished placental function and reserve. Intrauterine growth restriction (IUGR) which causes the infant to be malnourished is another associated condition. IUGR can be a result of maternal disease, placental disease, multiple gestation, connective tissue disorders, severe hypertension, and diabetes. Late or no prenatal care resulted in a higher risk of HIE. Certainly, illicit drug use could play a role. An abnormally appearing placenta increased the risk two-fold and boys had a 50% increased risk over girls. Birth defects were found in 23 % of those affected in this study compared to 2.3 % of those not affected with HIE. These defects may have made the brain more susceptible to injury. Abnormal fetal heart rates were found in 8.5% versus 2.0% of normal infants.