The internal contractile measure was the strength of the contractions based upon the sum of the contraction amplitudes measured at the anterior and posterior endometrial / myometrial interfaces. The amplitude at each interface was defined as the average difference between the endometrial / myometrial-lumenal distance measured at the peaks and troughs of the endometrial / myometrial interfaces. The internal contractile measure was reported in mm/contraction. The internal contractile measure quantified the movement of the endometrium relative to the lumen, i.e. the motion internal to the uterus.