The efficacy of individual computer heart rate indices in detecting acidemia at birth in growth-restricted fetuses

Objective: To determine the efficacy of individual fetal heart rate (FHR) indices, as determined by computer analysis of the FHR tracing, in detecting fetal acidemia at birth in growth-restricted fetuses. Methods: The study population consisted of 38 growth-restricted fetuses at 26-37 weeks' gestation from pregnancies with abnormal uterine and/or umbilical artery Doppler velocimetry. The 1-hour FHR tracing was analyzed by computer within 4 hours of cesarean birth before the onset of labor. Umbilical artery cord blood was collected at birth, and pH was determined within 5 minutes of collection. Results: On linear regression, the duration of episodes of low variation in minutes (r = -0.77, r(2) = 0.59) and short-term (r = 0.72, r(2) = 0.52) and long-term (r = 0.69, r(2) = 0.47) variation in milliseconds were significantly related to umbilical artery pH at birth, and more so than the number of accelerations of ten (r = 0.57, r(2) = 0.32) and 15 (r = 0.38, r(2) = 0.14) beats per minute. There were significant differences in computer measurements of FHR accelerations and variation between the umbilical artery pH categories of acidemia (pH less than 7.20), preacidemia (7.20-7.25), and nonacidemia (greater than 7.25). Stepwise regression revealed that episodes of low Variation best described the model for predicting umbilical artery pH at birth (P < .001), with no improvement provided by the addition of other computer-analyzed FHR characteristics. Conclusion: In this population of growth-restricted fetuses delivered by elective cesarean, the computer indices of duration of episodes of low variation and short-term and long-term variation were significantly associated with umbilical artery pH and predicted umbilical artery acidemia at birth.