Objective: To correlate the presence of baseline variability and the duration of a prolonged deceleration/bradycardia in intrapartum fetal heart rate (FHR) tracings with the development of neonatal acidemia.
Methods: We identified 186 patients with term gestations who had continuous electronic fetal monitoring for at least 2 hours before delivery, with an identified bradycardia during that period. Each patient had umbilical artery cord analysis done and delivery within 30 minutes of that bradycardia. One investigator blinded to the cord gas outcome reviewed the last 2 hours of the tracing using the National Institute of Child Health and Human Development guidelines for FHR monitoring. We assessed the presence or absence of variability before the bradycardia and recovery or no recovery of the bradycardia and placed the patients into four groups. Group 1 (128 patients) with normal variability and recovery, group 2 (40 patients) with normal variability and no recovery, group 3 (nine patients) with decreased variability and recovery, and group 4 (nine patients) with decreased variability and no recovery. We compared the incidence of neonatal acidosis defined as a pH of less than 7.0 at birth among the four groups. The relationship between the various groups was assessed using analysis of variance and the chi(2) test. In addition, a multiple logistic regression model was developed with the parameters of amplitude and recovery used to predict pH at birth.
Results: The presence of decreased variability and no recovery of the FHR of a bradycardia was associated with the lowest pH 6.83 +/- 0.16 and a 78% incidence of significant acidosis. Decreased variability before FHR bradycardia was the FHR parameter significantly correlated with low pH.
Conclusion: The most significant factor predicting the development of pathologic neonatal acidemia and indicating the need for urgent delivery in the presence of a bradycardia is decreased variability before the bradycardia.