| Accelerations | Visually apparent, abrupt (onset to peak < 30 seconds) increase in FHR from the most recently calculated baseline |
| Peak ≥ 15 bpm above baseline, duration ≥ 15 seconds, but < 2 minutes from onset to return to baseline; before 32 weeks’ gestation: peak ≥ 10 bpm above baseline, duration ≥ 10 seconds |
| Baseline FHR | Approximate mean FHR rounded to increments of 5 bpm during a 10-minute segment, excluding periodic or episodic changes, periods of marked variability, and segments of baseline that differ by > 25 bpm |
| In any 10-minute window, the minimum baseline duration must be ≥ 2 minutes, or the baseline for that period is indeterminate (refer to the previous 10-minute segment for determination of baseline) |
| Bradycardia | Baseline rate: < 110 bpm |
| Decelerations | |
| Early | The nadir of the deceleration occurs at the same time as the peak of the contraction |
| Late | The nadir of the deceleration occurs after the peak of the contraction |
| Variable | Abrupt decrease in FHR; if the nadir of the deceleration is ≥ 30 seconds, it cannot be considered a variable deceleration |
| Tachycardia | Baseline rate: > 160 bpm |
| Variability | |
| Absent | Amplitude range: undetectable |
| Minimal | Amplitude range: detectable, but ≤ 5 bpm |
| Moderate | Amplitude range: 6 to 25 bpm |
| Marked | Amplitude range: > 25 bpm |