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There are several labor abnormalities that may interfere with the orderly progression to spontaneous delivery. Generally, these are referred to as dystocia. Dystocia literally means difficult labor and is characterized by abnormally slow labor progress. It arises from four distinct abnormalities that may exist singly or in combination. First, expulsive forces may be abnormal. For example, uterine contractions may be insufficiently strong or inappropriately coordinated to efface and dilate the cervix—uterine dysfunction. Also, there may be inadequate voluntary maternal muscle effort during second-stage labor. Second, fetal abnormalities of presentation, position, or development may slow labor. Also, abnormalities of the maternal bony pelvis may create a contracted pelvis. And last, soft tissue abnormalities of the reproductive tract may form an obstacle to fetal descent. More simply, these abnormalities can be mechanistically simplified into three categories that include abnormalities of the powers—uterine contractility and maternal expulsive effort; the passenger—the fetus; and the passage—the pelvis. Common clinical findings in women with these labor abnormalities are summarized in Table 23-1.

TABLE 23-1Common Clinical Findings in Women with Ineffective Labor

Dystocia Descriptors

Abnormalities that are shown in Table 23-1 often interact in concert to produce dysfunctional labor. Commonly used expressions today such as cephalopelvic disproportion and failure to progress are used to describe ineffective labors. Of these, cephalopelvic disproportion is a term that came into use before the 20th century to describe obstructed labor resulting from disparity between the fetal head size and maternal pelvis. But the term originated at a time when the main indication for cesarean delivery was overt pelvic contracture due to rickets (Olah, 1994). Such absolute disproportion is now rare, and most cases result from malposition of the fetal head within the pelvis (asynclitism) or from ineffective uterine contractions. True disproportion is a tenuous diagnosis because two thirds or more of women undergoing cesarean delivery for this reason subsequently deliver even larger newborns vaginally. A second phrase, failure to progress in either spontaneous or stimulated labor, has become an increasingly popular description of ineffectual labor. This term reflects lack of progressive cervical dilatation or lack of fetal descent. Neither of these two expressions is specific. Terms presented in Table 23-2 and their diagnostic criteria more precisely describe abnormal labor.

TABLE 23-2Abnormal Labor Patterns, Diagnostic Criteria, and Methods of Treatment

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