Abnormal labor: Protraction and arrest disorders

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Abnormal labor: Protraction and arrest disorders

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Andrew J Satin, MD

Christian Macedonia, MD

UpToDate performs a continuous review of over 330 journals and other resources. Updates are added as important new information is published. The literature review for version 12.2 is current through April 2004; this topic was last changed on March 23, 2004.

INTRODUCTION – Labor refers to uterine contractions resulting in progressive dilation and effacement of the cervix and accompanied by descent and expulsion of the fetus. Abnormal labor, dystocia, and failure to progress are terms used to describe a difficult labor pattern that deviates from that observed in the majority of women who have spontaneous vaginal deliveries. This problem is the most common indication for primary cesarean birth, accounting for three times more cesarean deliveries than malpresentation or fetal heart rate abnormalities [1]. As an example, one study of 733 women with unplanned cesareans reported 68 percent were due to lack of progress in labor; the diagnosis was made after four centimeters dilation in 75 percent of the patients [2].

NORMAL LABOR – Friedman, in his classic studies, divided labor into three stages [3]:

• First stage: time from the onset of labor until complete cervical dilatation

• Second stage: time from complete cervical dilatation to expulsion of the fetus

• Third stage: time from expulsion of the fetus to expulsion of the placenta

The first stage was further subdivided into the latent and active phases, and the active phase subdivided into three additional phases: acceleration phase, phase of maximum slope, and deceleration phase (show figure 1).

Numerous investigations have confirmed that a rapid change in the rate (slope) of cervical dilation occurs at 3 to 4 centimeters when cervical dilatation is plotted against time. This is the beginning of the active phase. The existence of a latent phase and subphases of active labor are more controversial. Latent phase is typically characterized by mild, infrequent, irregular contractions with gradual change in cervical dilation (usually 1 cm hour) cervical change. (See "Prolonged latent phase of labor").

The median duration of the second stage of labor in nulliparous and multiparous women is 50 and 20 minutes, respectively. The upper limit of duration associated with a normal perinatal outcome had been defined as two hours [4], but was subsequently lengthened [5,6]. Epidural analgesia, duration of the first stage, parity, maternal size, birth weight, and station at complete dilation all play a role in predicting duration of the second stage [7]. However, a stepwise multiple linear regression demonstrated that these factors together accounted for less than 25 percent of observed variation in duration of the second stage [7]. For these reasons, the American College of Obstetricians and Gynecologists (ACOG) recommends that the normal duration of second stage of labor be based upon parity and presence of regional anesthesia, with no intervention as long as the fetal heart rate pattern is normal and some degree of progress is observed (show table 1) [6].

The total duration of labor also varies between nulliparous and parous parturients. One report of 25,000 women at term revealed the average duration of active labor (onset defined as 3 cm dilation) in nulliparous and parous women was 6.4 and 4.6 hours, respectively [8]. In addition, the labor curve of grand multiparas (para 5 or more) appears to differ from that of lower parity women: progress is slower prior to 6 cm [9].

Normal uterine activity – Uterine activity can be monitored by palpation, external tocodynamometry, or internal uterine pressure catheters. External and intrauterine monitoring devices appear to perform equally well, although the latter may work better in obese women [10].

Ninety-five percent of women in labor will have three to five contractions per 10 minutes. Although numerous methods for quantifying uterine activity have been reported, Montevideo units (ie, the peak strength of contractions in mmHg measured by an internal monitor multiplied by their frequency per 10 minutes) are most often employed. In a retrospective report, 91 percent of women in spontaneous active labor achieved contractile activity greater than 200 Montevideo units and 40 percent reached 300 Montevideo units [11].

CLASSIFICATION – One practical classification system to categorize labor abnormalities is shown in Table 1 (show table 1) [6]:

• Protraction disorders refer to slower-than-normal labor progress

• Arrest disorders refer to complete cessation of progress.

It is important to emphasize that the rates of cervical change listed in Table 1 are two standard deviations from the mean and thereby used to define abnormal; they do not represent the mean or median rates.

Progressive dilation slower than the rate shown in Table 1 is suggestive of a protraction disorder. An arrest disorder can be diagnosed when the cervix ceases to dilate after reaching four or more centimeters dilation despite a uterine contraction pattern of greater than or equal to 200 Montevideo units for two or more hours [6]. Protraction and arrest disorders may occur in both the first and second stage of labor.

INCIDENCE – In one large series, the incidence or protraction or arrest disorders in the first stage of labor was 13 percent [12], second stage abnormalities appeared to be as common [6].

Arrest disorders in the second stage of labor have received attention in the United States as a possible reason for differences in the cesarean delivery rates between the United States and Ireland, where active management of labor is practiced. As an example, four American trials of active management of labor (AML) found that the incidence of cesarean birth in the second stage was higher in the United States than at the National Maternity Hospital in Dublin (over 3 and 0.2 percent, respectively) [13-16]. Although active management of labor at the National Maternity Hospital has been associated with shorter labors and a cesarean delivery rate lower than that found at most hospitals in the United States, the cesarean delivery rate at that Institution has increased somewhat in recent years and the best controlled randomized trials to date do not show a decrease in cesarean birth associated with implementation of active management. (See "Active management of labor").

ETIOLOGY OF PROTRACTION AND ARREST DISORDERS – Abnormal labor can be the result of one or more abnormalities of the cervix, uterus, maternal pelvis, or fetus (ie, power, passenger, or pelvis). Risk factors for abnormal labor are shown in Table 2 (show table 2). Hypocontractile uterine activity is the most common cause of protraction or arrest disorders in the first stage of labor. This entity refers to uterine activity that is either not sufficiently strong or not appropriately coordinated to dilate the cervix and expel the fetus. It occurs in 3 to 8 percent of parturients and can be quantified as uterine contraction pressures less than 200 Montevideo units.

Dystocia related to epidural analgesia – The potential impact of epidural analgesia on uterine activity, fetal malposition, and, ultimately, arrest disorders has received much attention as a possible source of increasing rates of cesarean delivery. In a meta-analysis of eleven studies involving more than 3000 women, epidural analgesia was associated with an increased duration of the first and second stages of labor, incidence of fetal malposition, use of oxytocin, and operative vaginal delivery [17]. However, epidural anesthesia was not shown to increase the cesarean rate. This report was unable to determine whether certain types of epidural (narcotic or low-dose anesthetics) could decrease the incidence of dystocia. Consequences of withdrawing the block before the second stage of labor, appropriate use of oxytocin, delayed pushing in the second stage, and timing of administration also need to be considered. (See "Prevention and treatment of adverse effects of neuraxial anesthesia-I" section on Areas of controversy).

The American College of Obstetricians and Gynecologists has stated that the decision to place an epidural anesthetic depends upon the patient's wishes with consideration of factors, such as parity, also taken into account [18]. In particular, women should not be required to reach an arbitrary cervical dilation such as 4 to 5 cm before receiving epidural anesthesia.

Dystocia due to cephalopelvic disproportion – The disproportion between the size of the fetus relative to the mother can lead to a diagnosis of dystocia due to cephalopelvic disproportion (CPD). This diagnosis is currently based upon slow or arrested labor during the active phase. However, it is usually do to fetal malposition (eg, extended or asynclitic fetal head) or malpresentation (mentum posterior, brow), rather than a true disparity between fetal and maternal pelvic dimensions. (See "Fetal presentation in labor").

Prediction of CPD requiring cesarean delivery based upon clinical assessment of maternal (show figure 4A-B) versus fetal size (show figure 4C) has been disappointing . In a recent decision analysis and subsequent clinical study, a group of investigators found that in women without diabetes, the level of intervention and economic costs of prophylactic cesarean delivery for fetal macrosomia diagnosed by ultrasound are excessive [19,20]. A prophylactic cesarean delivery policy with either a 4000 or 4500 gram definition of macrosomia threshold would require more than 10,000 cesarean births and millions of dollars to prevent a single permanent brachial plexus injury. In addition, four trials of pelvimetry for fetal cephalic presentation at term in over 1000 women found that those undergoing pelvimetry were twice as likely to be delivered by cesarean [21]; no impact on perinatal outcome was detected. Thus, there is no evidence to support the use of radiographic pelvimetry in women with cephalic presentations.

Dystocia due to malposition – Over 95 percent of fetuses present in cephalic presentation at term. Approximately 5 percent of these experience malposition with persistent occiput posterior (OP) position or transverse arrest. In two studies including over 10,000 deliveries, persistent OP position was associated with a longer duration of active labor and second stage [22,23]. In another series of 16,781 nulliparas, persistent OP position was related to arrest of descent requiring operative delivery [24]. The rates of instrumental vaginal or cesarean delivery for OP position compared to occiput anterior (OA) were 44 and 24 percent rates (OP and OA instrumental deliveries) or 42 and 14 percent (OP and OA cesarean deliveries). Multiparous women with persistent OP are more likely to achieve spontaneous vaginal delivery than nulliparas (55 to 57 versus 26 to 29 percent) [23,25,26].

Pregnant women are often advised to perform exercises to facilitate anterior rotation of the fetus, but there is no good evidence that these maneuvers are effective. The lack of benefit was best illustrated by a large, multicenter, randomized, controlled trial that assigned 2547 women at 36 to 37 weeks of gestation to one of two exercise programs [27]. Group 1 was told to take a daily walk and Group 2 was asked to assume a hands and knees position with slow pelvic rocking for 10 minutes twice a day until labor began. The incidence of persistent OP position at birth or before instrumental rotation was similar in both groups (about 8 percent).

APPROACH TO THE PATIENT WITH ABNORMAL LABOR – Management of labor includes several components: a disciplined approach to the diagnosis of labor, careful monitoring of labor progress, and assessment of maternal and fetal well-being. Women should undergo cervical examination every one to two hours once active labor is diagnosed to determine whether progression is adequate [3]. Progress can be noted on a partogram (show figure 2).

Dystocia in the first stage:

• Amniotomy

• Hypo contractile uterine activity is treated with oxytocin

Numerous protocols varying in initial dose, incremental dose increases, and time intervals between doses have been studied (show table 2).

Oxytocin is typically infused to titrate dose to effect, as prediction of a women's response to a particular dose is not possible

Low dose regimens: (to avoid uterine hyperstimulation)

High dose regimens: (shorten labor )

Active phase arrest is diagnosed when a protraction disorder persists despite oxytocin therapy to achieve > or = 200 Montevideo units for greater than two hours; cesarean delivery is typically performed at this point. However, a trial in 542 women with an arrest or protraction disorder in which the obstetrician waited four to six hours (instead of two) before operating reported high vaginal delivery rates [31]. Vaginal deliveries occurred in 91 percent of parous women and 74 percent of nulliparas with an arrest or protraction disorder lasting two hours despite oxytocin administration and in 88 and 56 percent of multiparas and nulliparas, respectively, in whom the disorder lasted for four hours of oxytocin infusion. The authors concluded that extending the minimum period of oxytocin augmentation for active phase labor arrest from two to at least four hours was both effective and safe.

The same group subsequently used a standardized protocol to manage 501 consecutive term spontaneously laboring women with a protraction or arrest disorder [32]. The protocol involved use of an intrauterine pressure catheter and administration of oxytocin to achieve at least 200 Montevideo units for four hours before considering cesarean delivery. Vaginal delivery occurred in 85 percent of nulliparous women who sustained this threshold of uterine activity, 74 percent of those who achieved but were unable to sustain it, and in 83 percent of women who never achieved it. Corresponding figures for parous women were 94, 94, and 97 percent. Mean and 5th percentile rates of cervical dilatation were 1.4 and 0.5 cm/h in nulliparas and 1.8 and 0.5 cm/h in multiparas. This study confirmed that augmentation of a protraction disorder for at least four hours is both safe an effective for achieving vaginal delivery. It also showed that success was often possible despite levels of uterine activity and rates of cervical dilatation that were below the normal range considered effective.

Other interventions, such as ambulation [33] and continuous labor support, may increase the comfort of the parturient, but have not been shown to be clinically effective interventions for treatment of protraction or arrest disorders [6]. (See "Continuous intrapartum support").

Dystocia in the second stage – Risk factors include nulliparity, diabetes, macrosomia, epidural anesthesia, oxytocin usage, and chorioamnionitis [34].

• Continued observation.

• Attempt at operative vaginal delivery.

• Cesarean delivery.

Observation – Most women with a prolonged second stage ultimately deliver vaginally. In one study of 532 term singleton pregnancies with second stage over two hours, over 96 percent of patients who reached the second stage of labor delivered vaginally within 240 minutes [34] .The rates of vaginal delivery at 121 to 240 minutes and after 240 minutes were 90 and 66 percent, respectively [34]. Neonatal outcome was similar in pregnancies with second stages less than and greater than 120 minutes.

Dense motor blocks from epidural analgesia may impair a woman's ability to push. Thus, some authors have advocated turning down the epidural to facilitate progress during a prolonged second stage. As an example, one study of epidural anesthesia compared 0.125 percent bupivicaine versus saline infusion in the second stage and found saline was associated with a shorter second stage, fewer operative deliveries, but more pain [35].

Other noninvasive interventions that have been proposed include changes in maternal position [36,37], continuous emotional support of the parturient [38], delaying pushing if the fetal head is high in the pelvis at full dilatation and the woman has no urge to do so [39,40], and active management using high dose oxytocin. (See "Active management of labor").

Assisted vaginal delivery – (eg, extraction or rotation) Operative vaginal delivery and choice of instrument require careful assessment of the mother and fetus. Furthermore, success is dependent upon the training and skill of the obstetrician. A discussion of the indications, contraindications, use, and complications of instrumental deliveries is presented separately.

Occiput posterior position – Occiput posterior (OP) position is associated with a longer second stage, higher incidence of operative delivery, larger episiotomies, and more severe perineal lacerations than occiput anterior position [22,24,25]. A small increase in second stage length in the presence of a reassuring fetal heart rate, favorable clinical assessment of fetal relative to maternal size, and progress in the second stage does not mandate rotation or operative delivery.

The management of a definite arrest of descent of the OP fetus is not clear. No randomized trial of rotation to occiput anterior versus operative delivery from the OP position has been performed. Treatment options include operative delivery from OP position, manual or instrumental rotation to occiput anterior, or cesarean delivery. Our algorithm for managing these patients is shown in figure 4.

RECOMMENDATIONS – A general labor management algorithm is outlined in Figure 3 (show figure 3). The key points are listed below:

• Monitor progress in active labor with cervical exams at 1 to 2 hour intervals.

• If the patient in active labor fails to progress adequately for two hours, then intact membranes should be ruptured and oxytocin administered to achieve uterine contractions greater than 200 Montevideo units. These patients can be observed for two to four hours as long as clinical assessment of fetal and maternal size is favorable and the fetal heart rate is reassuring.

• The decision to perform an operative vaginal delivery (eg, extraction or rotation) in the second stage versus continued observation or cesarean birth is based upon clinical assessment of mother and fetus and the skill and training of the obstetrician.

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