Predictive value of electronic fetal monitoring for intrapartum fetal asphyxia with metabolic acidosis

Objective: To determine the predictive value of each fetal heart rate (FHR) variable and of patterns of FHR variables for fetal asphyxia during labor. Methods: This matched case-control study included an asphyxia group of 71 term infants with umbilical artery base deficit greater than 16 mmol/L and a control group of 71 term infants with umbilical artery base deficit less than 8 mmol/L. Each FHR record available for the 4 hours before delivery was scored in 10-minute cycles for each FHR variable. Selected patterns of important FHR variables were examined during the last hour before delivery for their predictive value for fetal asphyxia. Results: The FHR variables associated with fetal asphyxia included absent and minimal baseline variability and late and prolonged decelerations. Fetal heart rate patterns with absent baseline variability were the most specific but identified only 17% of the asphyxia group. The sensitivity of this test increased to 93% with the addition of less specific patterns. The estimated positive predictive value ranged from 18.1% to 2.6%, and the negative predictive value ranged from 98.3% to 99.5%. Conclusion: A narrow 1-hour window of FHR patterns including minimal baseline variability and late or prolonged decelerations will predict fetal asphyxial exposure before decompensation and newborn morbidity. Thus, with careful interpretation, predictive FHR patterns can be a useful screening test for fetal asphyxia. However, supplementary tests are required to confirm the diagnosis and to identify the large number of false-positive patterns to avoid unnecessary intervention. (Obstet Gynecol 1999;93:285-91. (C) 1999 by The American College of Obstetricians and Gynecologists.).