In most cases, the fetal monitoring system easily detects fetal heart rate. In some cases, such as if there is no fetal heart rate or if a maternal vessel is over the fetal heart, it may confuse the maternal pulse with the fetal heart rate. Particularly when the mother is under stress, her pulse can be elevated, causing it to fall within the range of a normal fetal heartbeat. This elevated pulse may make it more difficult for the clinician to notice signal ambiguity.
To prevent signal ambiguity from maternal heart rate, monitors perform coincidence detection. Coincidence detection continuously compares the maternal pulse or heart rate, as derived from maternal SpO2 or ECG measurements, to the fetal heart rate. When the two rates are the same, the monitor alerts the caregiver. All Philips Avalon Fetal Monitors perform this coincidence detection through a standard feature, called cross-channel verification (CCV).
While traditional coincidence detection is effective, it requires that SpO2 and/or ECG are measured with separate sensors and/or electrodes. This can be uncomfortable for the mother, requires additional work for the clinician, and is not always standard hospital protocol.