The Apgar score is universally used for fetal assessment at the time of birth, whereas, the collection of fetal cord blood gases is performed commonly in high-risk situations or in the setting of Apgar scores of <7, which is a less standardized approach. It has been well-established that neonatal acidemia at the time of delivery can result in significant neonatal morbidity and death. Because of this association, knowledge of the fetal acid-base status and detection of acidemia at the time of delivery can serve as a sensitive and useful component in the assessment of a neonate’s risk. Umbilical cord blood gas analysis is an accurate and validated tool for the assessment of neonatal acidemia at the time of delivery. Because the collection of fetal cord blood gases is not a standardized practice, it is possible that, with such a varied approach, some cases of neonatal acidemia are not detected, particularly in the setting of reassuring Apgar scores.

In a setting of universally obtained cord blood gases, we sought to identify the rates of acidemia and associated factors in neonates with 5-minute Apgar scores of ≥7.

This retrospective cohort study identified all term, singleton, nonanomolous neonates with 5-minute Apgar scores of ≥7. The incidence of umbilical artery pH ≤7.0 or ≤7.1 and base excess ≤–12 mmol/L or ≤–10 mmol/L were examined overall and in association with obstetric complications and adverse neonatal outcomes. Chi-squared tests were used to compare proportions, and multivariable logistic regression was used to control for potential confounders.

In this cohort, the incidence of an umbilical artery pH of ≤7.0 was 0.5%, of a pH ≤7.1 was 3.4%, of a base excess ≤–12 mmol/L was 1.4%, and of ≤–10 mmol/L was 4.0%. Rates of neonatal acidemia were greater in the setting of meconium (4.3% vs 3.2%; P<.001), placental abruption (13.2% vs 3.4%; P<.001), and cesarean deliveries (5.8% vs 2.8%; P<.001), despite normal 5-minute Apgar scores. Additionally, umbilical artery pH ≤7.0 was associated with an increased risk of respiratory distress syndrome (adjusted odds ratio, 6.5; 95% confidence interval, 2.9–14.3) and neonatal intensive care unit admission (adjusted odds ratio, 10.8; 95% confidence interval, 6.8–17.4). Base excess of ≤–12 mmol/L was also associated with an increased risk of neonatal sepsis (adjusted odds ratio, 4.7; 95% confidence interval, 1.9–12.1). Finally, when examined together, neonates with both a pH of ≤7.0 and base excess of ≤–12 mmol/L continued to demonstrate an increased risk of neonatal intensive care unit admission and respiratory distress syndrome, with adjusted odds ratios of 9.6 and 6.0, respectively. This risk persisted in neonates with a pH of ≤7.1 and base excess of ≤–10 mmol/L as well, with adjusted odds ratios of 4.5 and 1.1, respectively.

Because neonates with reassuring Apgar scores have a residual risk of neonatal acidemia that is associated with higher rates of adverse outcomes, the potential utility of obtaining universal cord blood gases should be further investigated.