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Diagnosis and Management of Arrest Disorders: Duration to Wait
Diagnosis and Management of Arrest Disorders: Duration to Wait Yasser Y. El-Sayed, MD To assess the thresholds of normal and protracted labor in contemporary US parturients. Select studies addressing first- and second-stage labor duration among contemporary cohorts of women in the United States were reviewed. Particular emphasis was placed on the work of the Consortium on Safe Labor. Duration of labor appears longer today than in the past. For both nulliparous and multiparous women, labor may take >6 hours to progress from 4 to 5 cm and >3 hours to progress from 5 to 6 cm of dilation. A cervical dilation of 6 cm appears to be a better landmark for the start of the active phase. The 95th percentile for duration of the second stage in a nulliparous woman with conduction anesthesia is closer to 4 hours. Current data on first and second stages of labor allow for an opportunity to reconsider traditionally accepted thresholds of normal and protracted labor, and thus affect consequent labor management paradigms. Semin Perinatol 36:374-378 © 2012 Elsevier Inc. All rights reserved. KEYWORDS labor, arrest, first and second stage
M
uch of our understanding of the stages of human labor is credited to the seminal work of Dr Emmanuel Friedman.1,2 He was the first to depict a labor curve divided into several stages and phases. He studied 622 consecutive primigravid women at term, 500 of whom were selected for analysis for sufficient detail and described the relationship between duration of labor and cervical dilation as a sigmoid curve.1 By defining the thresholds of normal labor, his work in the 1950s had a profound impact on labor management during the next many decades. Recent data in more contemporary patient cohorts offer an opportunity to revisit the diagnosis and management of arrest disorders in the first and second stages of labor.
The First Stage of Labor Friedman1 plotted 500 individual labor charts and synthesized them into a curve (Fig. 1). The latent phase was defined as the onset of regular uterine contractions to beginning of the active phase. The active phase heralded a change in the rate of dilation (slope) to full dilation and is itself divided into
Division of Maternal-Fetal Medicine and Obstetrics, Stanford University, Stanford, CA. Address reprint requests to: Yasser Y. El-Sayed, MD, Division of MaternalFetal Medicine and Obstetrics, Stanford University, Room HH333, 300 Pasteur Drive, Stanford, CA 94305. E-mail: yasser.el-sayed@stanford. edu
374
0146-0005/12/$-see front matter © 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1053/j.semperi.2012.04.022
acceleration phase, phase of maximum slope, and deceleration phase. This was followed by the second stage of labor. In nulliparas, the transition to active phase occurred by 4 cm, and the statistical minimum rate of dilation in the phase of maximum slope was 1.2 cm/h.1 In a separate study on multiparas, Friedman2 also described the transition to activephase labor occurring by 4 cm, with the statistical minimum rate of dilation in the phase of maximum slope being 1.5 cm/h. These threshold values have understandably become firmly entrenched in the obstetrical literature; however, several investigators have questioned their validity among more contemporary cohorts of women. Peisner and Rosen3 in 1986 analyzed 1060 nulliparous and 639 primi- or multiparous women in spontaneous labor with intact membranes on admission and suggested that the transition to active phase may occur later than described by Friedman. In their study, ⬍50% of labors were active by 4 cm and 74% were active by 5 cm. They concluded that “a patient who is not progressing in labor at 4 cm cervical dilation is not necessarily abnormal.” As pioneering as Friedman’s work was to obstetrics in the 1950s and beyond, the work by Zhang et al and the Consortium on Safe Labor, has greatly advanced and refined our understanding of the thresholds of normal labor in the modern era. In a retrospective study by Zhang et al4 of 1329 term, singleton, and nulliparous parturients with spontaneous onset of labor, vertex presentation, vaginal delivery, and normal birth weight, no perceivable change in cervical dilation for 2
Diagnosis and management of arrest disorders
375
Figure 1 The Friedman curve. Reprinted with permission from Friedman.1
hours before 7 cm was not uncommon. In addition, no deceleration phase was detected (this phase suggested as an artifact of missed observations), and the 5th percentiles for rate of cervical dilation in the active phase of labor were all ⬍1 cm/h. A subsequent study by Zhang et al5 for the Consortium on Safe Labor involved a retrospective review of electronic medical records from 19 hospitals across United States, involving 62,415 parturients. These were singleton gestations at term, with spontaneous onset of labor, vertex presenting fetus, a vaginal delivery, and a normal perinatal outcome. A repeated measures analysis was used to construct average labor curves by parity. Interval-censored regression was used to estimate duration of labor, and it was stratified by cervical dilation at admission and centimeter by centimeter. Median and 95th percentiles were then calculated for labor duration. They found that labor may take ⬎6 hours to progress from 4 to 5 cm and ⬎3 hours to progress from 5 to 6 cm of dilation. After
6 cm, labor accelerated for both nulliparous and multiparous women, although much faster in multiparous women than in nulliparous. As such, they conclude that the transition to the active phase of labor may be better defined at 6 cm cervical dilation in both nulliparous and multiparous women. Nulliparous woman had the longest and most gradual labor curve and may not have a clear active phase characterized by precipitous dilation (Table 1, Fig. 2). From these data, a connected staircase labor curve was generated based on both parity and cervical dilation at admission (women admitted at different dilation levels may have different patterns of progression). The right side of each curve represents the 95th percentile across time; as long as the rate of cervical dilation remains to the left of this threshold, the labor should not be considered protracted or arrested (Fig. 3). What is also important to highlight here is that data from the Consortium on Safe Labor indicate that among nulliparas
Table 1 Duration of Labor in Hours by Parity in Spontaneous Onset of Labor Cervical Dilation (cm)
Parity 0 (n ⴝ 25,624)
Parity 1 (n ⴝ 16,755)
Parity 2ⴙ (n ⴝ 16,219)
3-4 4-5 5-6 6-7 7-8 8-9 9-10 Second stage with epidural analgesia Second stage without epidural analgesia
1.8 (8.1) 1.3 (6.4) 0.8 (3.2) 0.6 (2.2) 0.5 (1.6) 0.5 (1.4) 0.5 (1.8) 1.1 (3.6) 0.6 (2.8)
— 1.4 (7.3) 0.8 (3.4) 0.5 (1.9) 0.4 (1.3) 0.3 (1.0) 0.3 (0.9) 0.4 (2.0) 0.2 (1.3)
— 1.4 (7.0) 0.8 (3.4) 0.5 (1.8) 0.4 (1.2) 0.3 (0.9) 0.3 (0.8) 0.3 (1.6) 0.1 (1.1)
Reprinted with permission from Zhang et al.5 Data are median (95th percentile).
376
Figure 2 Average labor curves by parity in singleton term pregnancies with spontaneous onset of labor, vaginal delivery, and normal neonatal outcomes. PO, nulliparous women; P1, women of parity 1; P2⫹, women of parity 2 or higher. Reprinted with permission from Zhang et al.5 (Color version of figure is available online.)
in spontaneous labor, 65% of intrapartum cesarean deliveries for dystocia were before 2nd stage and 28% were before 6 cm. Among nulliparas with induced labor, 81% of intrapartum cesarean deliveries for dystocia were before 2nd stage, and 53% before 6 cm.6 These values give weight to the assertion by Zhang et al7 that “our inability to reduce the cesarean delivery rate may be attributable in part to the incomplete understanding of a normal labor process, particularly in the first stage.” The American College of Obstetricians and Gynecologists practice bulletin from 2003 states that an arrest disorder in first stage of labor can be said to exist when the latent phase is completed, and the uterine contraction pattern exceeds 200 Montevideo units for 2 hours without cervical change.8 As discussed earlier in the text, the cervical dilation heralding the end of the latent phase has been questioned, as has the upper limit of time for cervical change. In fact Rouse et al,9 as far back as 1999, while still generally adhering to the traditional threshold of 4 cm for the beginning of active phase labor, advocated for at least 4 hours of ⬎200 Montevideo units or a minimum of 6 hours of oxytocin if that pattern was unattainable. By using this approach, the eventual vaginal delivery rate in a cohort of women with no progress after 4 hours of oxytocin was 56% for nulliparas and 88% for multiparas. The primary risk to this approach was chorioamnionitis. In fact, ACOG in the same 2003 publication adds that extending the minimum period of oxytocin augmentation for active-phase arrest from 2 to 4 hours appears effective.8 Given the data from the Consortium on Safe Labor (over 6 hours defining the 95th percentile of time to go from 4 to 5 cm cervical dilation, and an active-phase inflection at a cervical dilation of 6 cm not 4 cm),5 this approach and its associated success rates are in fact not surprising. In a similar vein, a recent Cochrane review highlights the importance of time in the context of traditional thresholds defining active labor. In this review, no treatment was as effective as oxytocin for “slow progress” in the first stage of labor—normal vaginal delivery relative risk 1.02 (95% confidence interval [CI]: 0.84-1.25).10 This either means that
Y.Y. El-Sayed oxytocin is not effective, or more likely reflects the fact that women who were simply given the appropriate amount of time progressed naturally into the active phase. Again, there appears to be a reasonable delta of safety in adopting a new paradigm for defining active-phase arrest in the first stage, not only as indicated in the Rouse et al trial9 but also as reaffirmed in the study by Cheng et al.11 In this retrospective analysis of 10,661 nulliparous women with term singleton gestations delivered in 1 academic center between 1990 and 2008, the primary risk of a first stage greater than the 95th percentile (beyond 30 hours) was a higher cesarean delivery rate (adjusted odds ratio [aOR]: 2.28, 95% CI: 1.35-2.14) and chorioamnionitis (aOR: 1.58, 95% CI: 1.25-1.98). The only increased risk to the neonate was a higher incidence of neonatal intensive care unit (NICU) admissions in the absence of any other of the major morbidities (aOR: 1.53, 95% CI: 1.18-1.97). In conclusion, labor appears to progress more slowly now than before. A more measured, nuanced approach to diagnosis of first-stage arrest is needed. Clinical management needs to be adjusted to account for the gradual active-phase curve in nulliparas and the later inflection point in multiparas. This can best be achieved in 2 ways: (1) use of 6 cm as a landmark for the start of the active phase. (2) Recognition that one curve does not fit all with the incorporation of the connected staircase labor curve based on both parity and admission dilation.
The Second Stage of Labor A 1950s article by Hellman and Prystowsky refers to admonitions by 2 distinguished obstetricians from the 1800s, Samuel Merriman and George Hamilton, regarding duration of the second stage. As quoted by Hellman and Prystowsky,12 in 1820, Merriman proclaimed that “the forceps shall never be applied until the ear of the child has been within the reach of
Figure 3 The 95th percentiles of cumulative duration of labor from admission among singleton term nulliparous women with spontaneous onset of labor, vaginal delivery, and normal neonatal outcomes. Reprinted with permission from Zhang et al.5 (Color version of figure is available online.)
Diagnosis and management of arrest disorders the operator’s fingers for at least six hours.” There appears to have been a revolt against this admonition by obstetricians fearing the fetal risks of such delay, and in 1861, Hamilton asserted that “Whenever the os has become fully dilated, so that an ear can be felt, I hold that the danger to the child becomes imminent if allowed to remain undelivered much more than 2 hours.”12 By the late 1800s, the 2 hour rule appears to have become firmly established in most American texts. Further support for this threshold also came from the work of Hellman and Prystowsky,12 who found an increase in infant mortality when second stage exceeded 150 minutes. Friedman’s data on the second stage, with a 55% rate of low or mid forceps, was more a consequence of these accepted paradigms as opposed to a study of the natural history of second-stage labor.1 An important contribution to our understanding of the normal thresholds of the second stage in a low-risk cohort of women was the study by Kilpatrick and Laros in 1989.13 In this retrospective review of nearly 7000 women with minimal intervention—all patients delivered spontaneously, none on oxytocin, all vertex, all term—the second stage in nulliparas was a mean of 54 minutes, 95th percentile 132 minutes without conduction anesthesia, and 95th percentile with conduction anesthesia 185 minutes. In multiparas, the respective values were 19 minutes, 61 minutes, and 131 minutes. These values are reflected in the thresholds for prolonged second stage of labor in the 2003 ACOG Practice Bulletin: Nulliparas: 2 hours without regional anesthesia, 3 hours with regional anesthesia. Multiparas: 1 hour without regional anesthesia, 2 hours with regional anesthesia.8 The Consortium on Safe Labor readdressed the 95th percentile for second-stage duration in their large aforementioned dataset.5 In that study, the 95th percentile for nulliparous women was 2.8 hours (168 minutes) without regional anesthesia and 3.6 hours (216 minutes) with regional anesthesia, further extending the threshold of normal duration of the second stage. For multiparous women, the 95th percentiles for second-stage duration with and without regional anesthesia remained around 2 and 1 hour, respectively. Irrespective of the statistical outer limit of normal secondstage duration, the question of maternal and neonatal safety at and beyond any such specified threshold remains a question of paramount importance. The 2003 ACOG Practice bulletin on dystocia and augmentation of labor instructs that “if progress is being made, duration of the 2nd stage alone does not mandate intervention by operative delivery.”8 However, how long is too long? Are there thresholds of time that once crossed compromise maternal and neonatal safety? Myles et al14 in a retrospective review of 6791 nulliparous women showed a progressively increasing risk of cesarean delivery (1.2% vs 16.1%), operative vaginal delivery (3.4% vs 21.3%), perineal lacerations (3.6% vs 16.3%), chorioamnionitis (2.3% vs 10.4%), and postpartum hemorrhage (2.3% vs 6.2%), with a second stage beyond 2 hours. Even beyond 4 hours, however, there were no increased neonatal morbidities. Similar findings were noted in a study by Cheng et al15 of 15,795 nulliparous, term, cephalic, singleton births at Uni-
377 versity of California, San Francisco between 1976 and 2001. Compared with women who delivered with a ⬍3 and ⬍4 hour second stage, women with second stages exceeding these benchmarks had an increased risk of chorioamnionitis (odds ratio [OR]: 1.79, 95% CI: 1.44-2.22), cesarean delivery (OR: 5.65, 95% CI: 4.46-7.16), operative vaginal delivery (OR: 2.83, 95% CI: 2.38-3.36), and 3rd and 4th degree lacerations (OR: 1.33, 95% CI: 1.07-1.67); once again, no increased risk of neonatal morbidities was noted. In a separate study on maternal cesarean delivery outcomes after a prolonged second stage, Sung et al16 found an increased risk of hysterotomy extensions into the cervix among women with a second stage exceeding 4 hours as compared with women with second stages between 1 and 3 hours (5% vs 29%, P ⫽ 0.005). However, questions regarding the neonatal risks of a prolonged second stage remain. Although confirming the general constellation of maternal risks with a progressively increasing duration of second stage, Rouse et al17 in a secondary analysis of the fetal pulse oximetry and cesarean delivery trial noted that admission to an NICU was associated significantly with second-stage duration (OR: 1.4). After controlling for mode of delivery, only one adverse neonatal outcome, brachial plexus injury, that was present at discharge, correlated with second-stage duration (aOR: 1.78, 95% CI: 1.08-2.78). However, the authors emphasize that the absolute risk of this was low (3/1000), and they conclude that the second stage of labor does not need to be terminated for duration alone. A different conclusion was reached by Allen et al,18 in their analysis of second-stage duration data out of the Nova Scotia Atlee Perinatal Database from 1988 to 2006. The cohort examined were term singleton pregnancies delivered in the second stage. Using standard definitions of prolonged second stage for nulliparas and multiparas, 11,470 (9%) of second stages were prolonged and 110,206 were not prolonged. Consistent with other studies, the risk of maternal morbidity was increased with longer second stage. Neonatal risks— birth depression, NICU admissions, and composite perinatal morbidity—were all increased, irrespective of mode of delivery, with second stages exceeding 2-3 hours in nulliparous women. However, the more nebulous category of NICU admissions was included in the other 2 measures of neonatal risk, and in fact when this was controlled for, the composite perinatal morbidity in nulliparous women no longer retained a significant association with length of the second stage, although significance was retained in multiparous women. Nonetheless, the authors conclude that the risks of both maternal and perinatal adverse outcomes rise with increased duration of the second stage, particularly for duration longer than 3 hours in nulliparous women and 2 hours in multiparous women. It is clear that the evidence is mixed in regards to the risks of a prolonged second stage. Maternal outcomes are worse, neonatal morbidities less evident. However, at least for maternal morbidities, it does not necessary follow that an earlier cesarean delivery would have reduced the spectrum of complications. In fact, an opposite argument could be made that a more liberal approach to operative intervention may exac-
Y.Y. El-Sayed
378 erbate these same maternal morbidities. Also, it is important to differentiate between association and causation. Is it simply that longer labor leads to more infections, or do women with pre-/subclinical chorioamnionitis have longer labors? Similarly, for postpartum hemorrhage and perineal lacerations—is it that longer labor leads to more bleeding/injury or is it that women with longer second stages eventually are delivered via cesarean and operative vaginal delivery leading to complications? The available literature does not address these issues directly. In fact, a systematic review of perinatal risks associated with a prolonged second stage by Altman et al19 described recurrent limitations to the available literature, including oversimplified categorization of the second stage, and inconsistency in study population characteristics and lack of control of confounding factors. The authors conclude by stating “the primary findings of our review indicated that most of the studies are flawed and do not answer the important questions for maternity caregivers to safely manage prolonged second stage.” It is also true that an approach informed by a concept that the “sky is the limit” for second-stage duration, is problematic if not for anything other than the marked decline in spontaneous vaginal delivery beyond a 4-hour second stage. In the previously mentioned second-stage study by Cheng et al,15 the rates of spontaneous vaginal delivery declined rapidly from ⬎80% in the 1-2 hour second-stage interval, to 57% in the 2-3-hour interval, to 18.8% in the ⬎4-hour interval and 16.4% past 6 hours. A spontaneous vaginal delivery rate of just 9% was noted past 5 hours of second stage in the secondary analysis of the fetal pulse oximetry study by Rouse et al.17 At which point for any given physician and patient do these diminishing odds of a spontaneous vaginal delivery favor intervention? Clearly prospective studies and data on long-term outcomes are needed to address second-stage management if we are to accurately understand maternal and neonatal risks of a second-stage duration of 3 hours in a nulliparous woman compared with 4, 5, or 6 hours. Furthermore, is the margin of maternal and neonatal safety for any given duration of labor maintained across the complex spectrum of delivery sites with varying volumes and resources? Until such time when this information is more evident, a new benchmark of 3.6 hours in a nulliparous woman with an epidural seems reasonable to define a prolonged second stage. Second-stage labor continuing past 4 hours in a nulliparous woman mandates precise assessment of actual descent and fetal status, balanced consideration of maternal and neonatal complications, and appreciation of the diminished likelihood of a spontaneous vaginal delivery. Within this context, an informed patient can then help guide decision making based on her personal preferences.
Conclusions Current data on first and second stages of labor allow for an opportunity to reassess traditionally accepted thresholds of normal labor and consequent management paradigms. By informing labor management with a more nuanced and measured understanding of the spectrum of what constitutes normal and what defines dystocia, it is in our capacity to safely reduce the inexorable increase in cesarean delivery and downstream maternal morbidities.
References 1. Friedman EA: Primigravid labor; a graphicostatistical analysis. Obstet Gynecol 6:567-589, 1955 2. Friedman EA: Labor in multiparas; a graphicostatistical analysis. Obstet Gynecol 6:691-703, 1956 3. Peisner DB, Rosen MG: Transition from latent to active labor. Obstet Gynecol 68:448-451, 1986 4. Zhang J, Troendle JF, Yancey MK: Reassessing the labor curve in nulliparous women. Am J Obstet Gynecol 187:824-828, 2002 5. Zhang J, Landy HJ, Branch DW, et al; Consortium on Safe Labor: Contemporary patterns of spontaneous labor with normal neonatal outcomes. Obstet Gynecol 116:1281-1287, 2010 6. Zhang J, Troendle J, Reddy UM, et al; the Consortium on Safe Labor: Contemporary cesarean delivery practice in the United States. Am J Obstet Gynecol 203:e1-10, 2010 7. Zhang J, Troendle J, Mikolajczyk R, et al: The natural history of the normal first stage of labor. Obstet Gynecol 115:705-710, 2010 8. American College of Obstetricians and Gynecologists Committee on Practice Bulletins-Obstetrics: ACOG practice bulletin, Number 49, December 2003: Dystocia and augmentation of labor. Obstet Gynecol 102:1445-1454, 2003 9. Rouse DJ, Owen J, Hauth JC: Active-phase labor arrest: Oxytocin augmentation for at least 4 hours. Obstet Gynecol 93:323-328, 1999 10. Bugg GJ, Siddiqui F, Thornton JG: Oxytocin versus no treatment or delayed treatment for slow progress in the first stage of spontaneous labour. Cochrane Database Syst Rev 7:CD007123, 2011 11. Cheng YW, Shaffer BL, Bryant AS, et al: Length of the first stage of labor and associated perinatal outcomes in nulliparous women. Obstet Gynecol 116:1127-1135, 2010 12. Hellman LM, Prystowsky H: The duration of the second stage of labor. Am J Obstet Gynecol 63:1223-1233, 1952 13. Kilpatrick SJ, Laros RK Jr: Characteristics of normal labor. Obstet Gynecol 74:85-87, 1989 14. Myles TD, Santolaya J: Maternal and neonatal outcomes in patients with a prolonged second stage of labor. Obstet Gynecol 102:52-58, 2003 15. Cheng YW, Hopkins LM, Caughey AB: How long is too long: Does a prolonged second stage of labor in nulliparous women affect maternal and neonatal outcomes? Am J Obstet Gynecol 191:933-938, 2004 16. Sung JF, Daniels KI, Brodzinsky L, et al: Cesarean delivery outcomes after a prolonged second stage of labor. Am J Obstet Gynecol 197:e1e5, 2007 17. Rouse DJ, Weiner SJ, Bloom SL, et al: Second-stage labor duration in nulliparous women: Relationship to maternal and neonatal outcomes. Am J Obstet Gynecol 201:e1-e7, 2009 18. Allen VM, Baskett TF, O’Connell MC, et al: Maternal and perinatal outcomes with increasing duration of the second stage of labor. Obstet Gynecol 113:1248-1258, 2009 19. Altman MR, Lydon-Rochelle MT: Prolonged second stage of labor and risk of adverse maternal and perinatal outcomes: A systematic review. Birth 33:315-322, 2006
M
uch of our understanding of the stages of human labor is credited to the seminal work of Dr Emmanuel Friedman.1,2 He was the first to depict a labor curve divided into several stages and phases. He studied 622 consecutive primigravid women at term, 500 of whom were selected for analysis for sufficient detail and described the relationship between duration of labor and cervical dilation as a sigmoid curve.1 By defining the thresholds of normal labor, his work in the 1950s had a profound impact on labor management during the next many decades. Recent data in more contemporary patient cohorts offer an opportunity to revisit the diagnosis and management of arrest disorders in the first and second stages of labor.
The First Stage of Labor Friedman1 plotted 500 individual labor charts and synthesized them into a curve (Fig. 1). The latent phase was defined as the onset of regular uterine contractions to beginning of the active phase. The active phase heralded a change in the rate of dilation (slope) to full dilation and is itself divided into
Division of Maternal-Fetal Medicine and Obstetrics, Stanford University, Stanford, CA. Address reprint requests to: Yasser Y. El-Sayed, MD, Division of MaternalFetal Medicine and Obstetrics, Stanford University, Room HH333, 300 Pasteur Drive, Stanford, CA 94305. E-mail: yasser.el-sayed@stanford. edu
374
0146-0005/12/$-see front matter © 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1053/j.semperi.2012.04.022
acceleration phase, phase of maximum slope, and deceleration phase. This was followed by the second stage of labor. In nulliparas, the transition to active phase occurred by 4 cm, and the statistical minimum rate of dilation in the phase of maximum slope was 1.2 cm/h.1 In a separate study on multiparas, Friedman2 also described the transition to activephase labor occurring by 4 cm, with the statistical minimum rate of dilation in the phase of maximum slope being 1.5 cm/h. These threshold values have understandably become firmly entrenched in the obstetrical literature; however, several investigators have questioned their validity among more contemporary cohorts of women. Peisner and Rosen3 in 1986 analyzed 1060 nulliparous and 639 primi- or multiparous women in spontaneous labor with intact membranes on admission and suggested that the transition to active phase may occur later than described by Friedman. In their study, ⬍50% of labors were active by 4 cm and 74% were active by 5 cm. They concluded that “a patient who is not progressing in labor at 4 cm cervical dilation is not necessarily abnormal.” As pioneering as Friedman’s work was to obstetrics in the 1950s and beyond, the work by Zhang et al and the Consortium on Safe Labor, has greatly advanced and refined our understanding of the thresholds of normal labor in the modern era. In a retrospective study by Zhang et al4 of 1329 term, singleton, and nulliparous parturients with spontaneous onset of labor, vertex presentation, vaginal delivery, and normal birth weight, no perceivable change in cervical dilation for 2
Diagnosis and management of arrest disorders
375
Figure 1 The Friedman curve. Reprinted with permission from Friedman.1
hours before 7 cm was not uncommon. In addition, no deceleration phase was detected (this phase suggested as an artifact of missed observations), and the 5th percentiles for rate of cervical dilation in the active phase of labor were all ⬍1 cm/h. A subsequent study by Zhang et al5 for the Consortium on Safe Labor involved a retrospective review of electronic medical records from 19 hospitals across United States, involving 62,415 parturients. These were singleton gestations at term, with spontaneous onset of labor, vertex presenting fetus, a vaginal delivery, and a normal perinatal outcome. A repeated measures analysis was used to construct average labor curves by parity. Interval-censored regression was used to estimate duration of labor, and it was stratified by cervical dilation at admission and centimeter by centimeter. Median and 95th percentiles were then calculated for labor duration. They found that labor may take ⬎6 hours to progress from 4 to 5 cm and ⬎3 hours to progress from 5 to 6 cm of dilation. After
6 cm, labor accelerated for both nulliparous and multiparous women, although much faster in multiparous women than in nulliparous. As such, they conclude that the transition to the active phase of labor may be better defined at 6 cm cervical dilation in both nulliparous and multiparous women. Nulliparous woman had the longest and most gradual labor curve and may not have a clear active phase characterized by precipitous dilation (Table 1, Fig. 2). From these data, a connected staircase labor curve was generated based on both parity and cervical dilation at admission (women admitted at different dilation levels may have different patterns of progression). The right side of each curve represents the 95th percentile across time; as long as the rate of cervical dilation remains to the left of this threshold, the labor should not be considered protracted or arrested (Fig. 3). What is also important to highlight here is that data from the Consortium on Safe Labor indicate that among nulliparas
Table 1 Duration of Labor in Hours by Parity in Spontaneous Onset of Labor Cervical Dilation (cm)
Parity 0 (n ⴝ 25,624)
Parity 1 (n ⴝ 16,755)
Parity 2ⴙ (n ⴝ 16,219)
3-4 4-5 5-6 6-7 7-8 8-9 9-10 Second stage with epidural analgesia Second stage without epidural analgesia
1.8 (8.1) 1.3 (6.4) 0.8 (3.2) 0.6 (2.2) 0.5 (1.6) 0.5 (1.4) 0.5 (1.8) 1.1 (3.6) 0.6 (2.8)
— 1.4 (7.3) 0.8 (3.4) 0.5 (1.9) 0.4 (1.3) 0.3 (1.0) 0.3 (0.9) 0.4 (2.0) 0.2 (1.3)
— 1.4 (7.0) 0.8 (3.4) 0.5 (1.8) 0.4 (1.2) 0.3 (0.9) 0.3 (0.8) 0.3 (1.6) 0.1 (1.1)
Reprinted with permission from Zhang et al.5 Data are median (95th percentile).
376
Figure 2 Average labor curves by parity in singleton term pregnancies with spontaneous onset of labor, vaginal delivery, and normal neonatal outcomes. PO, nulliparous women; P1, women of parity 1; P2⫹, women of parity 2 or higher. Reprinted with permission from Zhang et al.5 (Color version of figure is available online.)
in spontaneous labor, 65% of intrapartum cesarean deliveries for dystocia were before 2nd stage and 28% were before 6 cm. Among nulliparas with induced labor, 81% of intrapartum cesarean deliveries for dystocia were before 2nd stage, and 53% before 6 cm.6 These values give weight to the assertion by Zhang et al7 that “our inability to reduce the cesarean delivery rate may be attributable in part to the incomplete understanding of a normal labor process, particularly in the first stage.” The American College of Obstetricians and Gynecologists practice bulletin from 2003 states that an arrest disorder in first stage of labor can be said to exist when the latent phase is completed, and the uterine contraction pattern exceeds 200 Montevideo units for 2 hours without cervical change.8 As discussed earlier in the text, the cervical dilation heralding the end of the latent phase has been questioned, as has the upper limit of time for cervical change. In fact Rouse et al,9 as far back as 1999, while still generally adhering to the traditional threshold of 4 cm for the beginning of active phase labor, advocated for at least 4 hours of ⬎200 Montevideo units or a minimum of 6 hours of oxytocin if that pattern was unattainable. By using this approach, the eventual vaginal delivery rate in a cohort of women with no progress after 4 hours of oxytocin was 56% for nulliparas and 88% for multiparas. The primary risk to this approach was chorioamnionitis. In fact, ACOG in the same 2003 publication adds that extending the minimum period of oxytocin augmentation for active-phase arrest from 2 to 4 hours appears effective.8 Given the data from the Consortium on Safe Labor (over 6 hours defining the 95th percentile of time to go from 4 to 5 cm cervical dilation, and an active-phase inflection at a cervical dilation of 6 cm not 4 cm),5 this approach and its associated success rates are in fact not surprising. In a similar vein, a recent Cochrane review highlights the importance of time in the context of traditional thresholds defining active labor. In this review, no treatment was as effective as oxytocin for “slow progress” in the first stage of labor—normal vaginal delivery relative risk 1.02 (95% confidence interval [CI]: 0.84-1.25).10 This either means that
Y.Y. El-Sayed oxytocin is not effective, or more likely reflects the fact that women who were simply given the appropriate amount of time progressed naturally into the active phase. Again, there appears to be a reasonable delta of safety in adopting a new paradigm for defining active-phase arrest in the first stage, not only as indicated in the Rouse et al trial9 but also as reaffirmed in the study by Cheng et al.11 In this retrospective analysis of 10,661 nulliparous women with term singleton gestations delivered in 1 academic center between 1990 and 2008, the primary risk of a first stage greater than the 95th percentile (beyond 30 hours) was a higher cesarean delivery rate (adjusted odds ratio [aOR]: 2.28, 95% CI: 1.35-2.14) and chorioamnionitis (aOR: 1.58, 95% CI: 1.25-1.98). The only increased risk to the neonate was a higher incidence of neonatal intensive care unit (NICU) admissions in the absence of any other of the major morbidities (aOR: 1.53, 95% CI: 1.18-1.97). In conclusion, labor appears to progress more slowly now than before. A more measured, nuanced approach to diagnosis of first-stage arrest is needed. Clinical management needs to be adjusted to account for the gradual active-phase curve in nulliparas and the later inflection point in multiparas. This can best be achieved in 2 ways: (1) use of 6 cm as a landmark for the start of the active phase. (2) Recognition that one curve does not fit all with the incorporation of the connected staircase labor curve based on both parity and admission dilation.
The Second Stage of Labor A 1950s article by Hellman and Prystowsky refers to admonitions by 2 distinguished obstetricians from the 1800s, Samuel Merriman and George Hamilton, regarding duration of the second stage. As quoted by Hellman and Prystowsky,12 in 1820, Merriman proclaimed that “the forceps shall never be applied until the ear of the child has been within the reach of
Figure 3 The 95th percentiles of cumulative duration of labor from admission among singleton term nulliparous women with spontaneous onset of labor, vaginal delivery, and normal neonatal outcomes. Reprinted with permission from Zhang et al.5 (Color version of figure is available online.)
Diagnosis and management of arrest disorders the operator’s fingers for at least six hours.” There appears to have been a revolt against this admonition by obstetricians fearing the fetal risks of such delay, and in 1861, Hamilton asserted that “Whenever the os has become fully dilated, so that an ear can be felt, I hold that the danger to the child becomes imminent if allowed to remain undelivered much more than 2 hours.”12 By the late 1800s, the 2 hour rule appears to have become firmly established in most American texts. Further support for this threshold also came from the work of Hellman and Prystowsky,12 who found an increase in infant mortality when second stage exceeded 150 minutes. Friedman’s data on the second stage, with a 55% rate of low or mid forceps, was more a consequence of these accepted paradigms as opposed to a study of the natural history of second-stage labor.1 An important contribution to our understanding of the normal thresholds of the second stage in a low-risk cohort of women was the study by Kilpatrick and Laros in 1989.13 In this retrospective review of nearly 7000 women with minimal intervention—all patients delivered spontaneously, none on oxytocin, all vertex, all term—the second stage in nulliparas was a mean of 54 minutes, 95th percentile 132 minutes without conduction anesthesia, and 95th percentile with conduction anesthesia 185 minutes. In multiparas, the respective values were 19 minutes, 61 minutes, and 131 minutes. These values are reflected in the thresholds for prolonged second stage of labor in the 2003 ACOG Practice Bulletin: Nulliparas: 2 hours without regional anesthesia, 3 hours with regional anesthesia. Multiparas: 1 hour without regional anesthesia, 2 hours with regional anesthesia.8 The Consortium on Safe Labor readdressed the 95th percentile for second-stage duration in their large aforementioned dataset.5 In that study, the 95th percentile for nulliparous women was 2.8 hours (168 minutes) without regional anesthesia and 3.6 hours (216 minutes) with regional anesthesia, further extending the threshold of normal duration of the second stage. For multiparous women, the 95th percentiles for second-stage duration with and without regional anesthesia remained around 2 and 1 hour, respectively. Irrespective of the statistical outer limit of normal secondstage duration, the question of maternal and neonatal safety at and beyond any such specified threshold remains a question of paramount importance. The 2003 ACOG Practice bulletin on dystocia and augmentation of labor instructs that “if progress is being made, duration of the 2nd stage alone does not mandate intervention by operative delivery.”8 However, how long is too long? Are there thresholds of time that once crossed compromise maternal and neonatal safety? Myles et al14 in a retrospective review of 6791 nulliparous women showed a progressively increasing risk of cesarean delivery (1.2% vs 16.1%), operative vaginal delivery (3.4% vs 21.3%), perineal lacerations (3.6% vs 16.3%), chorioamnionitis (2.3% vs 10.4%), and postpartum hemorrhage (2.3% vs 6.2%), with a second stage beyond 2 hours. Even beyond 4 hours, however, there were no increased neonatal morbidities. Similar findings were noted in a study by Cheng et al15 of 15,795 nulliparous, term, cephalic, singleton births at Uni-
377 versity of California, San Francisco between 1976 and 2001. Compared with women who delivered with a ⬍3 and ⬍4 hour second stage, women with second stages exceeding these benchmarks had an increased risk of chorioamnionitis (odds ratio [OR]: 1.79, 95% CI: 1.44-2.22), cesarean delivery (OR: 5.65, 95% CI: 4.46-7.16), operative vaginal delivery (OR: 2.83, 95% CI: 2.38-3.36), and 3rd and 4th degree lacerations (OR: 1.33, 95% CI: 1.07-1.67); once again, no increased risk of neonatal morbidities was noted. In a separate study on maternal cesarean delivery outcomes after a prolonged second stage, Sung et al16 found an increased risk of hysterotomy extensions into the cervix among women with a second stage exceeding 4 hours as compared with women with second stages between 1 and 3 hours (5% vs 29%, P ⫽ 0.005). However, questions regarding the neonatal risks of a prolonged second stage remain. Although confirming the general constellation of maternal risks with a progressively increasing duration of second stage, Rouse et al17 in a secondary analysis of the fetal pulse oximetry and cesarean delivery trial noted that admission to an NICU was associated significantly with second-stage duration (OR: 1.4). After controlling for mode of delivery, only one adverse neonatal outcome, brachial plexus injury, that was present at discharge, correlated with second-stage duration (aOR: 1.78, 95% CI: 1.08-2.78). However, the authors emphasize that the absolute risk of this was low (3/1000), and they conclude that the second stage of labor does not need to be terminated for duration alone. A different conclusion was reached by Allen et al,18 in their analysis of second-stage duration data out of the Nova Scotia Atlee Perinatal Database from 1988 to 2006. The cohort examined were term singleton pregnancies delivered in the second stage. Using standard definitions of prolonged second stage for nulliparas and multiparas, 11,470 (9%) of second stages were prolonged and 110,206 were not prolonged. Consistent with other studies, the risk of maternal morbidity was increased with longer second stage. Neonatal risks— birth depression, NICU admissions, and composite perinatal morbidity—were all increased, irrespective of mode of delivery, with second stages exceeding 2-3 hours in nulliparous women. However, the more nebulous category of NICU admissions was included in the other 2 measures of neonatal risk, and in fact when this was controlled for, the composite perinatal morbidity in nulliparous women no longer retained a significant association with length of the second stage, although significance was retained in multiparous women. Nonetheless, the authors conclude that the risks of both maternal and perinatal adverse outcomes rise with increased duration of the second stage, particularly for duration longer than 3 hours in nulliparous women and 2 hours in multiparous women. It is clear that the evidence is mixed in regards to the risks of a prolonged second stage. Maternal outcomes are worse, neonatal morbidities less evident. However, at least for maternal morbidities, it does not necessary follow that an earlier cesarean delivery would have reduced the spectrum of complications. In fact, an opposite argument could be made that a more liberal approach to operative intervention may exac-
Y.Y. El-Sayed
378 erbate these same maternal morbidities. Also, it is important to differentiate between association and causation. Is it simply that longer labor leads to more infections, or do women with pre-/subclinical chorioamnionitis have longer labors? Similarly, for postpartum hemorrhage and perineal lacerations—is it that longer labor leads to more bleeding/injury or is it that women with longer second stages eventually are delivered via cesarean and operative vaginal delivery leading to complications? The available literature does not address these issues directly. In fact, a systematic review of perinatal risks associated with a prolonged second stage by Altman et al19 described recurrent limitations to the available literature, including oversimplified categorization of the second stage, and inconsistency in study population characteristics and lack of control of confounding factors. The authors conclude by stating “the primary findings of our review indicated that most of the studies are flawed and do not answer the important questions for maternity caregivers to safely manage prolonged second stage.” It is also true that an approach informed by a concept that the “sky is the limit” for second-stage duration, is problematic if not for anything other than the marked decline in spontaneous vaginal delivery beyond a 4-hour second stage. In the previously mentioned second-stage study by Cheng et al,15 the rates of spontaneous vaginal delivery declined rapidly from ⬎80% in the 1-2 hour second-stage interval, to 57% in the 2-3-hour interval, to 18.8% in the ⬎4-hour interval and 16.4% past 6 hours. A spontaneous vaginal delivery rate of just 9% was noted past 5 hours of second stage in the secondary analysis of the fetal pulse oximetry study by Rouse et al.17 At which point for any given physician and patient do these diminishing odds of a spontaneous vaginal delivery favor intervention? Clearly prospective studies and data on long-term outcomes are needed to address second-stage management if we are to accurately understand maternal and neonatal risks of a second-stage duration of 3 hours in a nulliparous woman compared with 4, 5, or 6 hours. Furthermore, is the margin of maternal and neonatal safety for any given duration of labor maintained across the complex spectrum of delivery sites with varying volumes and resources? Until such time when this information is more evident, a new benchmark of 3.6 hours in a nulliparous woman with an epidural seems reasonable to define a prolonged second stage. Second-stage labor continuing past 4 hours in a nulliparous woman mandates precise assessment of actual descent and fetal status, balanced consideration of maternal and neonatal complications, and appreciation of the diminished likelihood of a spontaneous vaginal delivery. Within this context, an informed patient can then help guide decision making based on her personal preferences.
Conclusions Current data on first and second stages of labor allow for an opportunity to reassess traditionally accepted thresholds of normal labor and consequent management paradigms. By informing labor management with a more nuanced and measured understanding of the spectrum of what constitutes normal and what defines dystocia, it is in our capacity to safely reduce the inexorable increase in cesarean delivery and downstream maternal morbidities.
References 1. Friedman EA: Primigravid labor; a graphicostatistical analysis. Obstet Gynecol 6:567-589, 1955 2. Friedman EA: Labor in multiparas; a graphicostatistical analysis. Obstet Gynecol 6:691-703, 1956 3. Peisner DB, Rosen MG: Transition from latent to active labor. Obstet Gynecol 68:448-451, 1986 4. Zhang J, Troendle JF, Yancey MK: Reassessing the labor curve in nulliparous women. Am J Obstet Gynecol 187:824-828, 2002 5. Zhang J, Landy HJ, Branch DW, et al; Consortium on Safe Labor: Contemporary patterns of spontaneous labor with normal neonatal outcomes. Obstet Gynecol 116:1281-1287, 2010 6. Zhang J, Troendle J, Reddy UM, et al; the Consortium on Safe Labor: Contemporary cesarean delivery practice in the United States. Am J Obstet Gynecol 203:e1-10, 2010 7. Zhang J, Troendle J, Mikolajczyk R, et al: The natural history of the normal first stage of labor. Obstet Gynecol 115:705-710, 2010 8. American College of Obstetricians and Gynecologists Committee on Practice Bulletins-Obstetrics: ACOG practice bulletin, Number 49, December 2003: Dystocia and augmentation of labor. Obstet Gynecol 102:1445-1454, 2003 9. Rouse DJ, Owen J, Hauth JC: Active-phase labor arrest: Oxytocin augmentation for at least 4 hours. Obstet Gynecol 93:323-328, 1999 10. Bugg GJ, Siddiqui F, Thornton JG: Oxytocin versus no treatment or delayed treatment for slow progress in the first stage of spontaneous labour. Cochrane Database Syst Rev 7:CD007123, 2011 11. Cheng YW, Shaffer BL, Bryant AS, et al: Length of the first stage of labor and associated perinatal outcomes in nulliparous women. Obstet Gynecol 116:1127-1135, 2010 12. Hellman LM, Prystowsky H: The duration of the second stage of labor. Am J Obstet Gynecol 63:1223-1233, 1952 13. Kilpatrick SJ, Laros RK Jr: Characteristics of normal labor. Obstet Gynecol 74:85-87, 1989 14. Myles TD, Santolaya J: Maternal and neonatal outcomes in patients with a prolonged second stage of labor. Obstet Gynecol 102:52-58, 2003 15. Cheng YW, Hopkins LM, Caughey AB: How long is too long: Does a prolonged second stage of labor in nulliparous women affect maternal and neonatal outcomes? Am J Obstet Gynecol 191:933-938, 2004 16. Sung JF, Daniels KI, Brodzinsky L, et al: Cesarean delivery outcomes after a prolonged second stage of labor. Am J Obstet Gynecol 197:e1e5, 2007 17. Rouse DJ, Weiner SJ, Bloom SL, et al: Second-stage labor duration in nulliparous women: Relationship to maternal and neonatal outcomes. Am J Obstet Gynecol 201:e1-e7, 2009 18. Allen VM, Baskett TF, O’Connell MC, et al: Maternal and perinatal outcomes with increasing duration of the second stage of labor. Obstet Gynecol 113:1248-1258, 2009 19. Altman MR, Lydon-Rochelle MT: Prolonged second stage of labor and risk of adverse maternal and perinatal outcomes: A systematic review. Birth 33:315-322, 2006