FACE PRESENTATION . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
BROW PRESENTATION . . . . . . . . . . . . . . . . . . . . . . . . . . 452 TRANSVERSE LIE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452 COMPOUND PRESENTATION ..................... 454 COMPLICATIONS WITH DYSTOCIA. . . . . . . . . . . . . . . . . 454 ... pains become less requent and less intense, although giving rise to quite as much or even more suering than previousy. At the same time, the cervix, which was becoming obliterated and dilated in a satiactory manner, ceases to make urther proress and labour apparenty comes to a stanstill.
-J.
he term dystocia as described by Williams in the irst edition of this text still applies today. It literally means dficult labor and is characterized by abnormally slow labor progress. Similar to the factors described by Williams, dystocia arises from three distinct abnormality categories. First, uterine contractions may be insuiciently strong or inappropriately coordinated to eface and dilate the cevix-uterine dyunction. lso, voluntary maternal muscle efort during second-stage labor may be inadequate. Second, fetal abnormalities of presentation, position, or anatomy may slow progress. Last, structural changes can contract the maternal bony pelvis. Or, soft tissue abnormalities of the reproductive tract may form an obstacle to fetal descent. More simply, these alterations can be mechanistically simplified into three categories that include abnormalities of the powers-uterine contractility and maternal expulsive efort; of the passenger-the fetus; and of the passage-the pelvis and lower reproductive tract.
23-1 oten interact singly or in combination to produce dysfunctional labor. Commonly used expressions today such as cephalopelvic disproportion and ailure to progress are used to describe inefective labors. Of these,
TABLE 23-1. Common Clinical Findings in Women with Ineffective Labor
Inadequate cervical dilation or fetal descent:
Fetopelvic disproportion:
Inadequate pelvic capacity Malpresentation or pOSition of the fetus Abnormal fetal anatomy 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 (0lah, 1994). Such absolute disproportion is now rare, and most cases result from malposition of the fetal head within the pelvis (asynclitism) or from inefective uterine contractions. True disproportion is a tenuous diagnosis because many women who undergo cesarean delivery for this reason subsequently deliver even larger newborns vaginally in subsequent pregnancies. A second phrase, ailure to progress in either spontaneous or stimulated labor, has become an increasingly popular description of inefectual labor. his term reflects lack of progressive cervical dilation or lack of fetal descent. Neither of these two terms is specific.
• Mechanisms of Dystocia
At the end of pregnancy, the fetal head encounters a relatively thick lower uterine segment and undilated cervix. With the . onset of labor, the factors influencing progress are uterine contractions, cervical resistance, and the forward pressure exerted by the leading fetal part.
Ater complete cervical dilation, the mechanical relationship between the fetal head size and position and the pelvic capacity, namelyetopelvic proportion, becomes clearer as the fetus attempts to descend. Because of this, abnormalities in fetopelvic proportions become more apparent once the second stage is reached.