In 2007, the cesarean delivery rate was 31.8 percent—the highest level ever reported for the United States (Hamilton and co-workers, 2009). According to the American College of Obstetricians and Gynecologists (2003), approximately 60 percent of primary cesarean deliveries in the United States are attributable to the diagnosis of dystocia. Roy (2003) has proposed that this high frequency results from environmental changes that are developing more rapidly than Darwinian natural selection. Humans are poorly adapted to the affluence of the modern diet, and one result is dystocia. Evidence in support of this comes from Barau and associates (2006), who analyzed prepregnancy body mass index (BMI) and the risk of cesarean delivery. They studied 16,592 singleton births and reported a linear association between BMI and cesarean delivery. This has been similarly shown by others (Leung, 2008; Nuthalapaty, 2004; Roman, 2008; Treacy, 2006; Wilkes, 2003, and all their colleagues). As further discussed in Chapter 43, Getahun and co-workers (2007) reported that obesity is associated with an increased cesarean delivery rate. Interestingly, these researchers found that a decrease in weight from obese to normal eliminates this risk.
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:
Abnormalities of the expulsive forces. 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.
Abnormalities of presentation, position, or development of the fetus.
Abnormalities of the maternal bony pelvis—that is, pelvic contraction.
Abnormalities of soft tissues of the reproductive tract that form an obstacle to fetal descent (see Chap. 40, Reproductive Tract Abnormalities).
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 20-1.
Table 20-1. Common Clinical Findings in Women with Ineffective Labor |Favorite Table|Download (.pdf)
Table 20-1. Common Clinical Findings in Women with Ineffective Labor
Inadequate cervical dilation or fetal descent:
- Protracted labor—slow progress
- Arrested labor—no progress
- Inadequate expulsive effort—ineffective pushing
- Excessive fetal size
- Inadequate pelvic capacity
- Malpresentation or position of the fetus
Ruptured membranes without labor
Combinations of the abnormalities shown in Table 20-1 often interact to produce dysfunctional labor. Today, expressions such as cephalopelvic disproportion and failure to progress often are used to describe ineffective labors:
The expression cephalopelvic disproportion came into use prior to the 20th century to describe obstructed labor resulting from disparity between the size of the fetal head and maternal pelvis. But the term originated ...