Table 1.

Wave direction system used in this research (as proposed by van Gestel et al. [29])

Number	Wave direction	Description
1	CF	Waves from cervix to fundus
2	FC	Waves from fundus to cervix
3	CF/FC	Waves from cervix to fundus and waves from fundus to cervix, alternating
4	CF recoiling	Waves from cervix to fundus, with a reflection of the wave toward the cervix after reaching the fundus of the uterine cavity
5	Standing	Movement visible, but the activity is not conducted toward fundus or cervix
6	Opposing	Waves starting simultaneously in fundus and cervix
7	Random	Movement activity starting at various foci of the uterine cavity
8	No act	No intra-uterine movement visible