The women have a pacemaker electrode placed vaginally. A 5 (1.67mm) or 6 (2.00mm) French electrode catheter with distal 4x2mm platinum alloy rings 5mm apart (C. R. Bard, Inc., Lowell, MA, USA) is manually placed into the posterior vaginal fornix next to the external cervical os. The catheter's proximal end is taped to the patient's thigh and its connecting cable attached to the pacemaker, which can generate a weak bipolar electrical current (0-20 mA, 0-50 msec/pulse, 50 Hz). In the study, the EI current is increased slowly, as needed, up to a maximum of 17 mA.