Table 1.

NICHD definitions of fetal heart rate parameters

Uterine activity: presence of contractions

Baseline fetal heart rate: approximation of the mean fetal heart rate of increments of 5 beats per minute (bpm), using a 10-minute window, and excluding periodic changes; at least 2 of 10 minutes must be spent at the baseline, or the baseline for that period is indeterminate Normal: 110–160 bpm Bradycardia: <110 bpm Tachycardia: >160 bpm

Baseline fetal heart rate variability: the visual quantification of amplitude of the fluctuations of the fetal heart rate at the baseline; thought to be a physiologic result of the interplay between fetal sympathetic and parasympathetic nervous systems Absent: undetectable amplitude Minimal: amplitude 1–5 bpm Moderate: amplitude 6–25 bpm Marked: amplitude >25 bpm

Accelerations: visually apparent abrupt increase in fetal heart rate, moving from baseline to peak in <20 seconds; must be at least 15 bpm above baseline and last at least 15 seconds

Decelerations: a visually apparent decrease in fetal heart rate at least 15 bpm below the baseline, and further classified by type Late deceleration: visually apparent, often symmetric, gradual decrease (onset to nadir ≥30 seconds) and return of fetal heart rate to baseline, but delayed- often with the onset, nadir, and resolution after the beginning, peak and end of the contraction Variable deceleration: visually apparent abrupt decrease in fetal heart rate, onset to nadir in <30 seconds, and return to baseline; onset, depth, and duration often vary when occurring with contraction Early deceleration: visually apparent, often symmetric, graduate increase (onset to nadir ≥30 seconds) and return of fetal heart rate to baseline associated with a uterine contraction, with the nadir occurring with the peak of contraction Prolonged deceleration: >2 minutes, by <10 minutes [>10 minutes is a baseline change]