Acidemia Can Occur Despite Category I Tracing

Abstract

Objective: Electronic fetal monitoring (EFM) is intended to assess fetal well-being during labor. Our objective was to test the hypothesis that findings of a category I tracing at any time in the 60 minutes prior to delivery would rule out neonatal acidemia.

Study design: This was a planned secondary analysis of a single-center prospective cohort study of 8,580 singleton pregnancies undergoing labor with nonanomalous infants at term. Monitoring was reviewed by obstetric research nurses at 10-minute intervals in the 60 minutes prior to delivery. The primary outcome was acidemia, defined as an umbilical cord arterial pH of 7.10 or less.

Results: Of the 4,274 patients included, 42 (0.98%) infants had acidemia at birth. Of the 42 infants with acidemia, 13 (31%) had category I tracings in the 30 minutes prior to delivery. Three (7%) infants had neonatal acidemia despite category I tracing for >40 minutes in the 60 minutes prior to delivery.

Conclusion: Even in the presence of category I tracing in the 60 minutes prior to delivery, neonatal acidemia can still occur. Periods of category I should be interpreted within the clinical context of a priori risk for acidemia, knowing that it does not completely rule out acidemia.