Fetal Responses to Hypoxemia and Asphyxia

Hypoxemia poses a significant threat to fetal survival and development, often leading to neurodevelopmental disabilities including cerebral palsy or death. However, predicting and intervening in these cases remains challenging, despite advancements like therapeutic hypothermia. Abnormal fetal heart rate patterns provide only weak predictions of risk of acidemia and associated outcomes. Although severe metabolic acidemia correlates more strongly with neonatal outcomes, many infants with acute hypoxic–ischemic encephalopathy present with milder abnormalities, highlighting the complexity of hypoxic events. Modern studies indicate that only a fraction of cases of cerebral palsy are directly linked to intrapartum hypoxia-ischemia, and that a significant proportion of severe cases develop antenatally. This chapter will explore the mechanisms through which fetal adaptation to hypoxemia operates, circumstances that lead to failure of adaptation and subsequent brain injury, and the factors influencing the fetus’s ability to mitigate damage from hypoxia–ischemia.