Table 5.

The association between spectral indexes and fetal breathing activity, study overview and results.

Study			Frequency bands		Analyses	LFabsolute			HFabsolute			LF/HF
References	GAa	FBSb	LF (Hz)	HF (Hz)	Specifications; unit	Breathing	Non-breathing	p-value	Breathing	Non-breathing	p-value	Breathing	Non-breathing	p-value
Groome et al. (1994)c	37.9 (±1.1)	F1	0.04–0.2	0.2–2.5	Power density; no units given	0.62	0.33	<0.05	0.77	0.42	0.001	0.81e	0.79e
Gustafson et al. (2011)d	36-38	F2+F4	0.08–0.2	0.4–1.7	Power density; bpm2	1.42	1.39	0.81	1.31	0.63	<0.001	1.08	2.21	0.004
Gustafson et al. (2012)c	>36	F2+F4	0.08–0.2	0.4–1.7	power density; ms2f	10.1	12.4	0.74	9.1	4.3	<0.001	1.1	3.2	<0.0001
Ortiz et al. (2013)cg	34 (±3.7)	None		0.3–2.0	Power density; ms2				15.6?	7.8	<0.001
Arias-Ortega et al. (2016)c	34.2 (±2.6)	None		0.5–1.5	AMPHF; ms2				4.47	2.24	<0.05

^aGestational age.

^bFetal behavioral state(39). 1F: quiet, brief gross body movements, mostly startles; 2F: active, frequent and periodic gross body movements; 4F: active, vigorous, continual activity including many trunk rotations.

^cMean.

^dMedian.

^eCalculated according to results given in the study.

^fCalculated by exp[log(power)].

^gBreathing: ≥ 40% breathing movements, non-breathing: <40% breathing movements.