Metabolic Acidemia in Live Births at 35 Weeks of Gestation or Greater

OBJECTIVE: To estimate the incidence of metabolic acidemia and assess its association with a variety of obstetric complications in a large cohort of singleton live births at 35 weeks of gestation or greater. METHODS: We analyzed obstetric complications and neonatal outcomes associated with metabolic acidemia in singleton newborns delivered at 35 weeks of gestation or greater. Metabolic acidemia was identified as an umbilical artery pH of less than 7.0 and a base deficit of 12 mmol/L or greater from umbilical cord blood gas analyses performed immediately after delivery. The primary outcome of interest was seizures in the immediate newborn period. RESULTS: Between January 1, 1988, and December 31, 2013, a total of 1,265 (3.9/1,000, 95% confidence interval [CI] 3.7-4.1) neonates were identified with metabolic acidemia among 323,027 live births with cord gas analysis. Virtually every recorded obstetric complication was significantly associated with metabolic acidemia. All measures of neonatal morbidity except necrotizing enterocolitis were also significantly increased in the presence of metabolic acidemia. Seizures occurred in 367 of 323,027 (1.1/1,000, 95% CI 1.0-1.3) neonates. Only 19.1% (95% CI 15.2-23.5%) occurred in those with metabolic acidemia. Among the 1,265 with metabolic acidemia, 70 were diagnosed with neonatal seizures, for a prevalence of 5.5% (95% CI 4.3-6.9) in the acidotic group. CONCLUSION: Neonatal acidemia at birth is rare in deliveries occurring at or after 35 weeks of gestation. Seizures occur in less than one in 10 newborns with metabolic acidemia. Approximately 80% of seizures in neonates at this gestational age occur in nonacidemic neonates.