Table 1. Characteristics of fetal heart rates and the 3-tier categorization system.

Parameter		Definition	Code
Baseline	Normal	≧110 bpm and ≤160 bpm	1
	Tachycardia	>160 bpm, ≧10 min	2
	Bradycardia	<110 bpm, ≧10 min	3
Baseline variability	Absent	<2 bpm	4
	Minimal	2–5 bpm	5
	Moderate	6–25 bpm	6
	Marked	>25 bpm	7
Acceleration		An increase ≧15 bpm, ≧15 sec and <2 min (≧32 wks)	8
Deceleration	Early	Onset to nadir ≧30 sec	9
		No lag time
	Late	Onset to nadir ≧30 sec	10
		Lag time (≧18 sec)
	Variable	Onset to nadir <30 sec	11
		A decrease ≧15 bpm, ≧15 sec and <2 min
	Prolonged	A decrease ≧15 bpm, ≧2 min and <10 min	12
	Recurrent	Deceleration ≧50% of uterine contractions in a 20-min window	13
Sinusoidal pattern		≧5 bpm and <15 bpm	14
		3–5 cycles/min, ≧20 min
Category I	1∩6 – (10∪11∪12∪14).
Category II	3 – (3∩4), 2, 5, 4 – (4∩13), 7, 12, 11∩13∩(5∪6), or 10∩13∩6
Category III	4∩3, 4∩13∩(10∪11), or 14

bpm, beats per minute.