Table 2.

The accuracy of interval measurement

Window length	$\overline{\text{Δ}}{\mathbf{T}}_{\mathbf{i}}\pm \mathbf{\text{SD}}$[ms]	$\overline{\mid \text{Δ}{\mathbf{T}}_{\mathbf{i}}}\mid$[ms]	Median (|ΔTi|) [ms]
1.5	1.48 ± 6.82	2.58	1.04
1.75	0.24 ± 3.35	1.73	1.00
2	0.18 ± 3.05	1.68	1.02
2.25	0.08 ± 3.51	1.82	1.07
2.5	0.09 ± 3.59	1.94	1.15
3	0.19 ± 3.67	2.11	1.30
3.5	0.33 ± 4.13	2.40	1.45
4	0.48 ± 4.54	2.70	1.60

The descriptive statistics of differences between intervals derived from the Doppler ultrasound signal and the reference direct fetal electrocardiogram. The results were obtained on the basis of 8945 interval measurements.