What does the fetal spiral electrode calculate the fetal heart rate from?

The fetal spiral electrode is a specific tool used to monitor the fetal heart rate during labor. It is designed to provide accurate information about fetal heart rate by directly measuring electrical signals from the fetal heart. The fetal spiral electrode calculates the fetal heart rate from the R to R interval, which is the time between successive R waves on the fetal electrocardiogram (ECG). This interval reflects the time between heartbeats and is crucial for determining the heart rate.

In contrast, the other options do not accurately describe the intervals relevant to calculating fetal heart rate in this context. The Q to T interval pertains to other aspects of cardiac cycle assessment but is not utilized for fetal heart rate calculations. Cardiac output is a broader measurement related to the overall efficiency of the heart and does not specifically equate to heart rate. The S to R interval is not a standard term used in fetal heart rate monitoring and does not accurately represent the measurement used by the fetal spiral electrode. Understanding these distinctions highlights the significance of the R to R interval in clinical practice for effective fetal heart monitoring.