Associations between metabolic acidosis at birth and reduced Apgar scores within the normal range (7-10): A Swedish cohort study of term non-malformed infants

Background Risks of neonatal and long-term neurological outcomes are influenced by metabolic acidosis at birth and by reduced Apgar scores, even within the normal range (7-10). Objective To analyse associations between metabolic acidosis at birth and risks of reduced Apgar scores within the normal range. Methods In a Swedish cohort of term non-malformed infants born between 2008 and 2013, we included 81 861 infants with information from cord blood gas analyses and Apgar score values of 7-10 at 1, 5, and 10 minutes. Poisson log-linear regression analyses were used to examine associations between metabolic acidosis at birth (defined as pH <7.05 or <7.10 and base deficit >= 12) and Apgar scores of 7, 8, and 9. Adjusted risk ratios (RRs) and risk differences (RDs) were calculated, using 95% confidence intervals (CI). Results Compared with infants without metabolic acidosis, the adjusted RR of an Apgar score of 9 at 5 minutes was 3.14 (95% CI 2.57, 3.84) in infants with metabolic acidosis (pH <7.05 as cut-off), and 10.13 (95% CI 7.63, 13.45) and 7.60 (95% CI 3.54, 16.33) for Apgar scores of 8 and 7, respectively. Corresponding RRs of Apgar scores at 10 minutes were also substantially increased. The magnitude of RDs varied, but was consistently increased. Both reduced Apgar scores and metabolic acidosis (pH <7.10) influenced neonatal morbidity. Conclusions Metabolic acidosis is associated with increased risks of reduced Apgar scores within the normal range. Due to international variations in the assessment of Apgar score, our findings need to be confirmed in other populations.