Objective. Birth asphyxia is recognized as an important cause of neonatal morbidity and mortality. Whether advances in perinatal care have altered the incidence of birth asphyxia is unknown. We determined the incidence of birth asphyxia diagnoses made over a 10-year period in California. Methods. In a population-based retrospective cohort study of 5 364 663 live births, we determined the incidence and case fatality of birth asphyxia between 1991 and 2000. Using a statewide administrative hospital discharge database, we identified all newborn admissions that generated a diagnosis of birth asphyxia (International Classification of Diseases, Ninth Revision, Clinical Modification codes 768.5, 768.6, or 768.9) or a diagnosis that overlaps with birth asphyxia, such as congenital encephalopathy or fetal distress. We determined incidence and in-hospital case fatality rates adjusted for birth weight and demographic characteristics and stratified by associated perinatal complications. Results. The 24 330 newborns who received a diagnosis of birth asphyxia yielded a population incidence of 4.5 per 1000 live births. Black ethnicity (relative risk [RR]: 1.3; 95% confidence interval [CI]: 1.2-1.3), male gender (RR: 1.2; 95% CI: 1.1-1.2), and low socioeconomic status (RR: 1.2; 95% CI: 1.1-1.2) all were associated with increased risk. The diagnosis of birth asphyxia decreased by 91% from 14.8 to 1.3 per 1000 live births during the study years. This decrease could not be explained by an increased diagnosis of overlapping conditions. Overall case fatality was 4%, and the majority of deaths in infants >2000 g occurred in the presence of congenital anomalies, cord abnormalities, or maternal hemorrhage. In newborns <2000 g, case fatality was highest in the presence of chorioamnionitis (48%). Conclusion. The diagnosis of birth asphyxia has decreased dramatically in recent years. The factors that are responsible for this decline are unclear and deserve additional investigation.
