BACKGROUND AND PURPOSE:

• Assumptions
  • Better use and recognition of fetal heart rate (FHR) patterns during labor would improve neonatal outcomes
  • There is a useful correlation between FHR patterns and fetal arterial pH
  • Arterial pH adequately reflects fetal tolerance of hypoxic stress during labor
• There is no long-term data correlating FHR patterns with neonatal outcomes
• Johnson et al. (Obstetrics & Gynecology, 2021) tested the assumption that the correlation between neonatal acidemia and short-term newborn condition is in fact poor, in which case a key assumption regarding the use of electronic fetal monitoring is incorrect 

METHODS:

• Retrospective cohort study
• Participants
  • Term | Singleton | Nonanomalous fetuses
  • Availability of complete umbilical artery cord gas values and Apgar scores
  • Delivered between 2012 and 2020
• Exposures
  • Umbilical cord gas values
  • Apgar scores
• Study design
  • Spearman correlation coefficients and receiver operating characteristic curves were calculated for various levels of umbilical artery pH, base excess, and Apgar scores
  • Review of records: Medical records of neonates undergoing total body cooling for presumed intrapartum hypoxic injury
• Primary outcome
  • Correlation between umbilical artery pH and base excess and Apgar scores

RESULTS:

• 29,787 deliveries
  • Cesarean delivery: 36% of entire cohort
  • Base excess >-4: 46%
  • Base excess <-12: 26%
  • Base excess between -12 to -4: 21%
• The correlation between cord pH and base excess and both 1- and 5-minute Apgar scores was weak to non-existent for all pH range subgroups
  • Correlation range: 0.064 to 0.213
• Receiver operating characteristic curve analysis suggested a cord pH value of 7.22 yields the best discrimination for prediction of a severely depressed newborn (5-minute Apgar score less than 4)
  • Area under the curve: 0.742 | Sensitivity 62% | Specificity 78% (considered ‘fair’)
• Cooling for presumed intrapartum hypoxia–ischemia
  • Underwent cooling: 7 neonates
  • Umbilical artery pH >7.15 (range 6.72–7.17): 3 newborns

CONCLUSION:

• There is a weak to non-existent correlation between umbilical cord pH and Apgar score, suggesting that individual fetuses vary widely in their tolerance for the metabolic acidemia of labor
• This suggests that there may not be a path to “better” FHR use as a method of predicting fetal tolerance of labor
• Cesarean delivery in women with greater base deficit was lower, which may indicate that “ the wrong women often undergo cesarean delivery”
• The authors state that the data do not suggest a change in current intrapartum management, however

We believe this variability, rather than shortcomings of, or errors in pattern interpretation, to be the weak link in the chain responsible for the observed increased rate of cesarean delivery with no measurable reduction in long-term adverse outcomes

Under these circumstances, further refinements in pattern interpretation, although potentially improving the prediction of fetal pH, are unlikely to significantly alter these clinical outcomes

As far as our current approach to FHR interpretation, it would appear that this is as good as it gets

Learn More – Primary Sources:

Relationship Between Umbilical Cord Gas Values and Neonatal Outcomes: Implications for Electronic Fetal Heart Rate Monitoring

Related ObG Topics:

Planned Cesarean: Is Neonatal Cord pH Related to the Length of Time Between Spinal Anesthesia Placement and Delivery?

Meta-Analysis: Does Maternal Supplemental Oxygen at Delivery Improve Neonatal Outcomes?

Which Fetal Heart Monitoring Parameters Best Predict Fetal Acidemia?