Optimizing and validating an EMG-based fetal monitor to identify true preterm labor

Pretel, Inc., Chattanooga TN

Investigators

Linked publications, trials & patents

Abstract

External fetal monitoring is an irreplaceable clinical tool for moment-to-moment assessment of fetal well-being. It is performed by simultaneously measuring the fetal heart rate and uterine contractions. For 50 years, the fetal heart rate has been measured using the Doppler ultrasound and uterine contractions have been assessed using the tocodynamometer (Toco). The Doppler is an electronic stethoscope and the Toco is plunger-driven device that measures the uterine shape change that occurs with a contraction. Both the Doppler and the Toco are unreliable in preterm and obese patients. Toco only reports the timing of contractions, not the contraction strength, and cannot distinguish between false and true labor. Our overarching goal is to improve the reliability of fetal monitoring, especially for challenging patients such as obese or preterm, or both obese and preterm. Further, we will validate our method of determining if a patient is in true labor or false labor. We will accomplish this by applying new knowledge to an old technology ? uterine EMG. The uterus emits bioelectrical signals with each contraction that can be detected by electromyography (EMG), but only recently has EMG technology approached the reliability of Toco in reporting contractions. There are now four devices marketed for fetal monitoring that use this technology, and both use several ECG pads to record small uterine EMG signals. Although FDA cleared, the benefits of these devices over Doppler/Toco methods are slight. There remains significant need to improve the reliability of fetal monitoring, and especially to correctly identify contractions as true or false labor. This application is based on our advanced understanding of how the uterus generates coordinated contractions without a pacemaker or dedicated electrical conduction pathways. We show that contractions of the uterine muscle create an electric field that is directed perpendicular to the skin, rather than parallel with the skin, as has long-been assumed. To efficiently observe these signals, we created a novel directional EMG sensor, we call the ?area sensor?. Our prototype gathers 5 times the uterine bioelectrical signal, when compared to ECG pad-type electrodes. In this work, we propose to first optimize sensor design to increase sensor efficiency and signal. To accomplish this, we will vary the electrode size, width, and surface area to create 26 related designs, then test each design on ?phantoms? made of hydrogel that mimic human fat. We will then use the best design on preterm and obese patients to learn the monitoring capabilities in the most challenging patients. Finally, we will use 7 sensors to directly observe how well the local contractions are synchronized (highly synchronized predicts true labor, unsynchronized predicts false labor). Then we will check this prediction against that patient?s progress over the ensuing 24 hours. These data will validate the ability to separate false and true labor, which has never before been accomplished using non- invasive methods.