A number of other physiological conditions of the mother and baby during labor can be monitored in order to determine the progress of labor. These conditions include: (1) effacement (the thinning out of the cervix that occurs before and during the first stage of labor); (2) cervical dilatation (the increase in size of the cervical opening); (3) position of the cervix (the relation of the cervix to the vaginal axis, normally the fetal head); (4) station (the level of a predetermined point of the fetal presenting part with reference to the mother's pelvis), (5) position of the head which describes the relationship of the head to the pelvis and (6) and presentation which describes the part of the fetus (such as brow, face or breech) at the cervical opening.
Systems and methods have been proposed for monitoring the progress of labor. For example, U.S. Pat. Nos. 6,200,279 and 6,669,653 to Paltieli, incorporated herein by reference in their entirety, describe methods and apparatus for monitoring the progress of labor. In one embodiment, the progress of labor is monitored by attaching a position sensor to a predetermined point on the mother's pelvic bones, monitoring the location of the position sensor in three-dimensional space relative to a reference, and monitoring the location of the fetal presenting part with respect to the predetermined point on the mother's pelvic bones. The location of the fetal presenting part may be indicated by a similar position sensor, or by imaging. Other conditions, such as effacement, cervical dilatation, and cervical position may also be monitored in a similar manner.