Rates of metabolic acidosis at birth and Apgar score values at 1, 5, and 10 min in term infants: a Swedish cohort study.

Background Metabolic acidosis, measured in arterial umbilical cord blood at birth, is the most accepted definition of birth asphyxia. The aim of the study was to investigate the rates of metabolic acidosis across the entire range of Apgar score values (0-10) at 1, 5, and 10 min in term infants. Methods In a population-based Swedish cohort of births between 2008 and 2013, we included 85,076 term (≥37 weeks) non-malformed infants with information from umbilical arterial blood gas analyses and complete information on Apgar scores (0-10) at 1, 5, and 10 min. Results Rates of metabolic acidosis generally decreased with increasing Apgar score values. For Apgar score at 1 min, this decrease was consistent from Apgar score 0 (35%) to Apgar score 10 (0%). For Apgar scores at 5 and 10 min, the decrease was consistent for Apgar score values from 6 to 10. Conclusion Although there is a close association between Apgar score values and rates of metabolic acidosis, Apgar score is not and should not be used as a measure of birth asphyxia.