In active labor, disorders are divided into slower-than-normal progress-a protraction disorder-or complete cessation of progress-an arrest disorder. Terms presented in Table 23-2 and their diagnostic criteria more precisely describe abnormal labor. To be diagnosed with either of these, a woman must be in the active phase of labor, which is defined by cervical change.
hese criteria and management of abnormal labor have recently undergone a sea change. In 2014, the American College of Obstetricians and Gynecologists and the Society for vIaternal-Fetal Medicine issued their irst Obstetric Care Consensus titled Sae Prevention of the Primary Cesarean Delivery. It was reairmed in 2016. his consensus statement was a response to concerns that cesarean delivery was overused in the United States. Namely, approximately one in three women who give birth each year undergoes this surgery (Fig. 31-1, p. 592). New recommendations from the Consensus Committee are based on
TABLE 23-2. Abnormal Labor Patterns, Diagnostic Criteria, and Methods of Treatment
Arrest Disorders Prolonged deceleration phase Secondary arrest of dilation Arrest of descent Failure of descent
CPo = cephalopelvic disproportion. Modified from Cohen, 1983.
<l.2scm/hr 1.5 cm/hr Expectant and Cesarean delivery for CPD >2 hr >2 hr Evaluate for cpo: > 1 hr > 1 hr CPO: cesarean
No descent in deceleration No CPD: oxytocin "more recent data used to revise the definition of contemporary normal labor progress" and reflect a signiicant revision of the preexisting understanding of abnormal labor.
Active-Phase Protraction. Of active-phase disorders, protraction disorders are less well described, and the time necessary before diagnosing slow progress is undefined. he Wodd Health Organization (1994) has proposed a labor management partograph in which protraction is defined as < 1 cm/ hr cervical dilation for a minimum of 4 hours. hese criteria were adapted from those of Cohen and Friedman (1983) and shown in Table 23-2. For this disorder, observation for further progress is appropriate treatment. If insuicient Montevideo units are noted, oxytocin augmentation is initiated. According to the Consensus Committee (2016), slow but progressive irststage labor should not be an indication for cesarean delivery.
Active-Phase Arrest. Handa and Laros (1993) diagnosed active-phase arrest, deined as no dilation for 2 hours or more, in 5 percent of term nulliparas. This incidence has not changed since the 1950s (Friedman, 1978). Inadequate uterine contractions, deined as less than 180 Montevideo units, calculated as shown in Figure 23-1, were diagnosed in 80 percent of women with active-phase arrest. Hauth and coworkers (1986, 1991)
FIGURE 23-' Montevideo units are calculated by subtracting the baseline uterine pressure from the peak contraction pressure for each contraction in a 1 O-minute window and adding the pressures generated by each contraction. In the example shown, there were five contractions, producing pressure changes of 52,50,47,44, and 49 mm Hg, respectively. The sum of these five contractions is 242 Montevideo
Final study sample n 62,41e5
FIGURE 23-2 Study cohort for the analysis of spontaneous labor in the Consortium on Safe Labor study. NICU = neonatal intensive care unit. (Data from Zhang, 2010.) reported that when labor is efectively induced or augmented with oxytocin, 90 percent of women achieve 200 to 225 Montevideo units, and 40 percent achieve at least 300 Montevideo units. hese results suggest that certain minimums of uterine activity should be achieved before performing cesarean delivery for dystocia.