Performance of a condensed electrode patch compared to a diffuse electrode array for transabdominal fetal heart rate and uterine contraction monitoring: a preliminary report
Objective: Intrapartum monitoring of the fetal heart rate (FHR), maternal heart rate (MHR) and uterine activity (UA) can be done noninvasively via adhesive electrodes on the parturient’s abdominal surface. This approach, requiring multiple electrodes placed at specific positions on the abdomen, performs at least as well as ultrasound and tocodynamometry-based monitoring. We tested whether a single adhesive electrode template (a “patch”), which would simplify use and obviate errors in electrode placement, would function as well as diffusely arrayed single electrodes. Methods: Seventeen healthy term parturients were monitored simultaneously with a diffuse electrode array and a condensed array patch, each connected to an identical electronic processor. Equivalence of the two electrode systems was determined by comparing their success rate, percent agreement and percent equivalence for FHR and MHR detection. UA monitoring was assessed by comparing the percent agreement and sensitivity of the systems. Results: The success rates of the multiple electrode array and the patch for FHR and MHR detection were above 96%. The reliability of the patch was statistically equivalent to the standard electrode array. The percent agreement for FHR was 94.7 ± 4.0% and for MHR was 92.8 ± 5.3%. These were not affected by maternal body mass index or whether it was early or late labor. The percent equivalence for both FHR and MHR was above 98% indicating equivalence of the patch with the diffuse electrode array in the accuracy of heart rate detection. The percent agreement of UA detection between the patch and the electrode array averaged 98% and was not influenced by whether it was early or late labor. The sensitivity of the patch for detecting individual contractions was 86.1%, equivalent to the standard electrode array. However, the sensitivity was lower in early compared to late labor (82.1 ± 13.9 vs. 90.3 ± 9.3%; P=0.052). The lower 95% confidence limit in early labor (74.9%) fell below the 80% limit necessary for equivalence. Conclusion: The performance of an electrode patch template for intrapartum monitoring of fetal and maternal heart rate and uterine contractions was equivalent to that of a more diffuse electrode array in almost all respects
