Intrapartum fetal asphyxia: definition, diagnosis, and classification.

Evidence of a significant metabolic acidosis, an umbilical artery base deficit > 12 mmol/L, confirms that an asphyxial exposure has occurred. This is observed at delivery in approximately 2% of all pregnancies. Classification of the severity of the asphyxial exposure is difficult because the duration and nature of the exposure and the characteristics of the fetal cardiovascular response to the asphyxia in the affected fetus is usually not known. A classification is proposed in which the exposure to asphyxia is confirmed by a blood gas and acid-base assessment with evidence of a significant metabolic acidosis and the severity is defined by newborn encephalopathy and other organ system complications. Outstanding issues that may enhance this classification are identified.