The indirectly obtained fetal heart rate: comparison of first- and second-generation electronic fetal monitors.

Fetal heart rate variability has become an essential component in evaluation of the fetus during continuous electronic fetal monitoring. Because of technical deficiencies of monitoring equipment, fetal heart rate variability may not always be available, such as during indirect monitoring of the fetus. In lieu of integration, a mathematical procedure called autocorrelation has, with the use of microprocessors, been incorporated into the fetal monitor, creating the "second generation" of electronic fetal monitoring. This study examined the accuracy of the first- and second-generation monitors by comparing simultaneously obtained indirect and direct real-time fetal heart rate data. The second-generation monitor produced an indirectly obtained fetal heart rate that was more accurate when compared with the directly obtained data than that with the first-generation fetal monitor. In addition, the variation in data from the first-generation monitor was substantially higher than that with the second-generation monitor. It is concluded that the fetal heart rate tracing from the second-generation monitor is more accurate when compared with the fetal electrocardiogram and may facilitate a truer interpretation of fetal heart rate variability than that obtained with the first-generation monitor.