Cervical "Resistance" Measurements - a Novel Method for Evaluation of Cervical "Ripeness" Prior to Labor Induction

The investigators routinely use the Cook balloon catheter 13 for mechanical induction of labor 10-11 - this is a medical grade, double balloon catheter, comprised of a slender, flexible tube open at one end and closed at the opposite end; an inflatable distal balloon fixed to the tube at its closed end and designed to be inflated in the uterus; an inflatable proximal balloon located slightly below the uterine balloon (labeled as the cervical balloon).

The catheter will be inserted according to the manufacturer's instructions with the patient in a lithotomy position under visualization of the cervix. When both balloons are inserted, the uterine balloon will be inflated through valve V1; using 40 ml of sterile saline solution. With a slight downward pull on the catheter, the cervical balloon will be located inside the cervix. In order to measure the cervical resistance, the investigators will connect a sensitive, passive pressure gauge to the cervical inflated balloon with the use of a by a bi-directional valve. At this point the investigators will gradually inflate the cervical balloon via valve V2 with 80 ml of sterile saline solution. The cervical resistance will be measured and documented every 10 ml. Finally, the uterine balloon will be further inflated with additional saline to a volume of 40 ml. (as per our standard mechanical induction protocol). The investigators believe that this system provides an objective and quantifiable evaluation of the pressure exerted on the cervical balloon as it is gradually inflated. As the cervical stiffness ("resistance") increases the pressure within the cervical balloon will be higher with a given volume of fluid within it. Therefore, the investigators define cervical resistance as the pressure vs. volume curve within the cervical balloon.

A group of 100 patients, (50 multiparas & 50 nulliparas) with an obstetrical or medical indication for induction of labor will be recruited and consented for participation in this study. A transvaginal ultrasound will be performed prior to the initiation of the procedure to exclude placenta previa and to confirm a vertex presentation. Cervical length and angle will be recorded. All women will undergo a pelvic examination in order to obtain an initial Bishop Score.