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Perils of the new labor management guidelines Wayne R. Cohen, MD; Emanuel A. Friedman, Med ScD
T
he seemingly inexorable increase in the use of cesarean delivery, and the substantial contribution that dystocia and related diagnoses have made to that increase, have prompted a reevaluation of what constitutes normal labor.1-4 As a result, new guidelines promulgated jointly by the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) were released.5 The new recommendations define abnormal labor and provide guidelines for its management that differ sharply from those originally described by Friedman,6-10 which have formed the basis of the clinical management of labor for many decades in the United States and elsewhere. For that reason, a thorough analysis of the proposed standards is warranted to ensure that changes recommended for obstetric care during labor are justified by the available evidence. The guidelines are based heavily on analytic methods used by Zhang and colleagues11-14 to describe the patterns of cervical dilatation and fetal descent as functions of time elapsed in labor. Their findings, which have been rapidly adopted in some parts the obstetric community, have not yet been validated. For the reasons we briefly summarize in this commentary, we believe the new ACOG/SMFM recommendations From the Department of Obstetrics and Gynecology, University of Arizona College of Medicine, Tucson, AZ (Dr Cohen); and the Department of Obstetrics, Gynecology, and Reproductive Biology, Harvard Medical School, Boston, MA (Dr Friedman). Received Aug. 11, 2014; revised Aug. 20, 2014; accepted Sept. 2, 2014. The authors report no conflict of interest. Corresponding author: Wayne R. Cohen, MD. [email protected] 0002-9378/$36.00 ª 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.ajog.2014.09.008
Recent guidelines issued jointly by the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine for assessing labor progress differ substantially from those described initially by Friedman, which have guided clinical practice for decades. The guidelines are based on results obtained from new and untested methods of analyzing patterns of cervical dilatation and fetal descent. Before these new guidelines are adopted into clinical practice, the results obtained by these unconventional analytic approaches should be validated and shown to be superior, or at least equivalent, to currently accepted standards. The new guidelines indicate the patterns of labor originally described by Friedman are incorrect and, further, are inapplicable to modern obstetric practice. We contend that the original descriptions of normal and abnormal labor progress, which were based on direct clinical observations, accurately describe progress in dilatation and descent, and that the differences reported more recently are likely attributable to patient selection and the potential inaccuracy of very high-order polynomial curve-fitting methods. The clinical evaluation of labor is a process of serially estimating the likelihood of a safe vaginal delivery. Because many factors contribute to that likelihood, such as cranial molding, head position and attitude, and the bony architecture and capacity of the pelvis, graphic labor patterns should never be used in isolation. The new guidelines are based heavily on unvalidated notions of labor progress and ignore clinical parameters that should remain cornerstones of intrapartum decision-making. Key words: active phase, arrest of descent, arrest of dilatation, arrest of labor, deceleration phase, dysfunctional labor, labor curve, partogram
provide definitions of dysfunctional labor and guidelines for its management that, however well intentioned, are likely to impose undue risk on mother and fetus.
Historical background Prior to the mid-1950s, the evaluation of progress in labor was based primarily on its duration. Vague admonitions such as, “Never let the sun set twice on a laboring woman,” which were based on prevailing observations about average labor duration and outcomes,15 were commonly intoned. This approach was, however, ineffective in identifying when intervention would be appropriate or optimal. In 1954, the first of hundreds of studies of labor by, or based on the work of, Emanuel Friedman6 was published. Friedman’s work built upon previous investigators’ attempts to describe the events of labor as a function of
time.16-18 Their recognition of the practical implications of this approach was hampered by what we now know to have been erroneous assumptions about labor, particularly with regard to the role of membrane rupture. The first publications6-8 describing the graphic patterns of dilatation and descent stimulated the interest of many investigators, and led to the formulation of criteria that made the assessment of progress in labor objective rather than arbitrary.9,10,19-26 Unfortunately, the criteria have not always been applied appropriately, in part because of some misunderstandings about the curves and their proper place in clinical care.
Misconceptions It has often been alleged that Friedman’s seminal observations regarding the labor curves rest on a fragile foundation because they were never corroborated by others. In fact, numerous studies done
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in different parts of the world over the course of several decades confirmed the basic nature of the original curves, and validated their usefulness in clinical practice.27-43 There have been disagreements over the importance of the latent phase or even the existence of the deceleration phase of dilatation, but the core finding that active-phase cervical dilatation progresses linearly, with a lower limit of normal approximately 1.0 cm/h in nulliparas, has been remarkably consistent among studies. It is also noteworthy that in many institutions the introduction of labor curves to clinical care was associated with a decline in the cesarean rate.30,33,34 Some of the early data were collected using a mechanical cervimeter to obviate the potential subjectivity in clinical examination,9,44,45 and cervimetry by investigators using various tools confirmed the sigmoid nature of the dilatation curve.46-49 Limited data from more recently developed techniques to automate cervical assessment also appear consistent with the earlier observations.50,51 Sigmoid-shaped curves of cervical dilatation have even been described in cows, suggesting a common pattern of labor among mammalian species.52 Given the large body of evidence confirming the basic pattern of progress in normal labor, it is difficult to believe that labor progresses very differently today from how it was originally described. Why, then, do the labor curves of Zhang and his colleagues differ from those of previous observers? One explanation was provided by Zhang himself when he and his colleagues applied their analytical methods to the very same data Friedman had analyzed from the Collaborative Perinatal Project.14 Friedman’s analysis of those data revealed a sigmoid-shaped dilatation curve; that of Zhang et al revealed an exponential curve, essentially the same as they had found from contemporary labors. Clearly, what had changed was not the nature of progress in labor, but how the data were analyzed. This raises the question of which analytic technique provides a more accurate model of labor progress: that of Friedman or that of Zhang et al?
ajog.org In trying to address that question it is important to understand that the original dilatation and descent curves were based on and confirmed by direct experimental observations made on women in labor. The primacy of direct observation over theoretical conceptualization or indirect analysis of data in hypothesis testing has been a central tenet of the scientific method since the Enlightenment. When the results of an analytic approach differ from those derived from observation, it is important to understand why this has occurred, and try to adjudicate accordingly, before declaring the direct objective findings invalid. Analytical issues The labor curves in Friedman’s original reports were not created by using complex mathematical formulae, as some have suggested.2 The initial data were collected by a single observer.6 Subsequently, data from multiple practitioners in a single institution were reported.7,8 In both instances, the curves were drawn by hand, the descriptions were empiric, and the statistical analysis basic. Only later was a more sophisticated method of assessing the labor graphs by computer used to analyze >10,000 nulliparas from multiple institutions.53-56 This more sophisticated analysis confirmed the initial findings regarding the nature of the cervical dilatation and head descent time functions. The computer algorithm used was developed with the Office of Biometry of the National Institutes of Health. Raw labor data were plotted on a probit (ie, the normal probability) scale, to convert the sigmoid curves to straight lines.57,58 The maximum slope data were converted to logarithms to normalize their right-skewed distribution. The linearity thus achieved made the data amenable to descriptive statistical study for determining distributions and limits of normal, which have until recently stood the tests of time and clinical applicability. By contrast, Zhang and colleagues used a high-order polynomial curvefitting program to analyze dilatation and descent data, and interval-censored
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regression to fit curves based on centimeter-by-centimeter median traverse times. We have concerns about the application of this technique to labor. We do not profess personal expertise in this area, but we are impressed by the negative comments and strong skepticism encountered in the engineering literature pertaining to the limitations of high-order curve-fitting methods.59 Such models do not guarantee reliable results. Indeed, high-order curve fitting may not be appropriate or even necessary for most situations. Low-order quadratic curve fitting is preferable, whenever possible, and yields results that are at least as accurate. In fact, the higher the order, the less satisfactory curvefitting accuracy tends to be. This is so because ‘noise’ (ie, unstable data points, especially if those points are spread apart from each other or are located at the ends of the range of data) is magnified. As a consequence, portions of the derived curve are distorted. In this regard a leading authority opined that, “It is important to keep the order of the model as low as possible.As a general rule the use of high-order polynomials (k >2) should be avoided unless they can be justified for reasons outside the data.Arbitrary fitting of high-order polynomials is a serious abuse of regression analysis.”59 Zhang et al used polynomial curve-fitting models of the order of 810, far in excess of the cited recommendation of no higher than 1 or 2. Other investigators have used interval data to create labor curves, with varying results. Gurewitsch et al60 found a sigmoid curve of dilatation, but Chen and Chu61 found results similar to those of Zhang et al in terms of curve shape and much lower rates of dilatation. Thus, the differences alleged to exist between the Friedman and the Zhang curves are likely due to the different mathematical models used to fit these curves. This is confirmed by Zhang’s finding, noted above, that the same data Friedman and Neff62 analyzed decades ago yielded exponential curves with the curve-fitting methods used by Zhang and his colleagues.14 The approach by Zhang et al is likely to have introduced an important set of
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ajog.org selection biases, which also cast doubt on the validity of their findings. Women with rapidly progressing labors tend to present themselves for obstetric care and be first examined at more advanced cervical dilatation than those with longer labor. Thus, the intervals at the distal end of the dilatation curve are likely to have been loaded with progressively more rapid labors. This may explain the exponential nature of the dilatation curve derived in this manner. It may also explain why the descent curve, which was unencumbered by that problem because all patients were present and under observation for their entire second stage, looks very much like that originally reported.11 In addition, the labor curves of Zhang et al were generated after excluding women delivered by cesarean. Many of these were undoubtedly having slow, dysfunctional labor patterns that led to a diagnosis of dystocia and the need for cesarean delivery. Their exclusion is likely, therefore, to have falsely increased the average rate of dilatation in residual study cases, contributing to the exponential appearance of the curves. Zhang et al also excluded women whose cervix was >6 cm dilated at admission, probably thus excluding many of the most rapid labors and contributing to the overall appearance of slow average dilatation. In fact, these and other biases were acknowledged by Zhang and his colleagues.63 They stated that the fact that their study excluded first-stage cesareans “limit[ed] the generalizability of the results.” They also acknowledged the probable disparity in dilatation rates among parturients admitted at different time points in labor, thus raising doubts about the comparability of data derived from these sequential points. They further reported that their labor curves “are unadjusted for potential confounders, such as oxytocin use. While it is technically possible to control for confounders.it complicates the interpretation of the results..” They also acknowledged that “.time intervals for more advanced cervical dilation were affected to an extent by dropout of women because of caesarean delivery for
labor arrest. Such dropouts usually are not random. Slow progressing labors often dropped out early, making the average time intervals for the remaining women appear shorter than otherwise. The degree of bias depends on the incidence of first-stage caesarean delivery. Unfortunately, we have not yet recognized an easy solution to overcome this informed censoring.” To summarize, Zhang and colleagues have themselves acknowledged that both the selection biases and the unadjusted confounders likely influenced the shape of their dilatation curve either by slowing the early aspects of the active phase (or the transition from latent to active phase) or speeding the late aspects of the active phase, or both. The combined effect of these biases probably explains in part their finding that the rate of active-phase dilatation increases exponentially, rather than linearly as Friedman and many others have previously found.6-10,25-31,35-46 Transition to active phase One critically important way in which the new guidelines depart from the old is in identifying the transition from latent to active phase during the first stage. It is widely, but erroneously, concluded from the Friedman dilatation curve that the active phase of labor begins at 4 cm. Some studies have even used 3 cm as the definition of entry into active phase.64-66 According to the guidelines, the active phase begins at 6 cm. The difference is of critical importance, because it has a dramatic effect on whether dysfunctional labor can be diagnosed early in the active phase. Important labor abnormalities (protracted active phase and arrest of dilatation) that would be identified by the Friedman curve prior to 6 cm of dilatation would be classified as normal by the new guidelines. Why the active phase of first-stage labor has been inferred to begin at 4 cm is puzzling. We, in fact, have never suggested that the active phase begins at either 4 or 3 cm of cervical dilatation; on the contrary, we have expressly discouraged the use of any specific degree of dilatation for the identification of the
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active phase.23 Observations of dilatation data make it clear the active phase can begin anywhere from 3-6 cm, and, occasionally, earlier or later, depending on the individual labor.23,41 Using an arbitrary cutoff sacrifices accuracy for ease, and this unnecessary oversimplification risks incorrect diagnosis. The transition from the latent phase to the active phase can be correctly identified only by interpretation of serial clinical examinations for each patient as her labor progresses. Consider, for example, a labor that begins with the cervix 2 cm dilated for several hours. It then dilates rapidly to 5 cm in 1 hour, but fails to dilate further over the next 2 hours. According to the new guidelines, that would be normal latent-phase labor. To us it is an arrest of dilatation in active-phase labor that requires thorough evaluation to search for a cause. The likelihood that it will resolve itself (as many arrest disorders do) or would benefit from oxytocin stimulation would depend on the clinical circumstances, determinable by evaluation of mother and fetus. If there were significant molding and a narrow pelvis, little would be gained by further labor, and the fetus might be exposed to unnecessary risk.67,68
Diagnosis of arrest of dilatation Under the new guidelines, neither protracted active phase nor arrest of dilatation should be diagnosed in a nullipara before 6 cm cervical dilatation, and the lower limit of normal active-phase dilatation is about 0.5 cm/h, rather than the 1.0 or 1.2 cm/h reported by Friedman and others. The guidelines do recognize that there can be slow but progressive first-stage dilatation (protracted active phase), and that it should not be an indication for cesarean delivery, but they conflate protracted active phase and arrest of dilatation, despite evidence that they may be distinct disorders that respond differently to therapy and have a different prognosis.10,23 A protracted active phase, unless it has been caused by factors that inhibit contractility, such as anesthesia, infection, and (possibly) obesity, does not respond to oxytocin stimulation with an increased rate of
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dilatation. Contractility does, however, increase, thus conferring risk with no offsetting benefit.69-71 Role of contractile force To diagnose arrest of dilatation, the guidelines require that the cervix be 6 cm dilated, the membranes be ruptured, and there be no progress for 4 hours with adequate contractions, or 6 hours with inadequate contractions produced by oxytocin. They define adequate uterine contractility as “e.g., >200 Montevideo Units” (MVU), but recommend no alternative means of assessment. Moreover, no upper boundary of MVU is provided, thus condoning the potential exposure of the fetus to excessive uterine contractility. The definition also implies that an internal uterine pressure transducer (IUPT) is useful to diagnose an arrest of dilatation, but this is questionable. The use of MVUs is problematic for several reasons. Intrauterine catheters carry risk, and there is not evidence for benefit. Studies have demonstrated that the use of IUPTs had no advantage when compared to noninvasive means of assessing uterine contractility during labor.72-74 In addition, IUPT readings may depend on patient position, or on their location within the uterus and, most importantly, they do not correlate well with progress in cervical dilatation70,75 or with the need for cesarean delivery.69 Normal progress in dilatation is achieved over a broad range of uterine activity, and the pattern of contractions may be as important as their strength.76 The definition of arrest of dilatation proposed by the guidelines would, for example, allow a labor arrested at 8 cm with strong contractions to continue for at least 4 hours (and an additional 4 hours if the membranes were not ruptured until after the first 4 hours) at that dilatation before an arrest could be diagnosed and the recommended 4 hours of treatment begun. This recommendation would be inadvisable in many circumstances, because it fails to consider any preceding labor abnormalities, the results of clinical cephalopelvimetry, the presence of infection, and other factors that might be
ajog.org contributing to the dysfunction, some of which might not be surmountable. Of even more concern, the recommendations in the guidelines implicitly deny the possibility that the fetus could be put at risk by prolonged exposure to strong uterine contractions during an arrest of labor.67,68,77
Treatment of arrest of dilatation We have always taught, based on objective findings, that arrest of dilatation should generally be treated with oxytocin infusion unless there is compelling clinical evidence of disproportion or another contraindication to oxytocin use.23 Although the duration of oxytocin treatment should be tailored to the individual situation, a trial of about 4 hours was recommended as early as 1963.9,78 This approach was confirmed as appropriate more recently by other investigators.65 Several analyses of arrest of dilatation made it clear that the disorder will sometimes resolve spontaneously, but that oxytocin stimulation is often necessary, and usually effective.10,24,78 When oxytocin is used, about 90% of labors that will respond with further dilatation will have done so after 3-4 hours; 7 hours may be necessary before all cases have responded. Rupture of membranes seems to be effective in provoking further sustained dilatation in only a small proportion of cases.10,66 Given the risks associated with rupture of membranes (infection, abnormal fetal heart rate patterns, increased head compression66,68,79) we do not recommend amniotomy as a treatment for arrest disorders, but it should be used if there are other potential benefits, such as better quality fetal heart rate monitoring or more effective clinical evaluation. The deceleration phase During the terminal portion of the active phase of labor (the deceleration phase), uterine contractions remain strong, and the patient may perceive pain of increasing intensity. The graphic appearance of dilatation at this time, however, seems to slow. This results from the cervix being retracted in a
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cephalad direction (relative to the mother) around and alongside the fetal head. As it nears full dilatation, the cervix is no longer opening in a primarily transverse plane relative to the mother’s pelvis. Because our examination only measures dilatation accurately in that plane, dilatation appears to decelerate, even though the cervical rim is still being retracted at about the same speed as before. The deceleration phase is often quite short in normal labors and is easily missed if examinations are not done with sufficient frequency to identify it. The labor patterns reported by Zhang et al11,12 failed to show a deceleration phase, but they did acknowledge that it was present in cases delivered by cesarean that they had excluded from their analysis. In other words, its absence in their average curves was a consequence of patient selection. They excluded the very labors most likely to manifest prolonged deceleration. The presence of the deceleration phase has been confirmed by others.43,49,60,80-83 Despite the artificial nature of the deceleration phase of the dilatation curve, it reflects a critically important time in labor. Deceleration generally marks the beginning of fetal descent, and its prolongation portends significant problems for the labor. Frequent careful examinations during this portion of labor can yield important prognostic insights regarding the risk of shoulder dystocia, abnormal secondstage descent, and the likelihood of the need for cesarean delivery.82-86
The second stage The new guidelines define normal limits for the second stage by elapsed time after full cervical dilatation, and take no account of the rate of fetal descent. Using only elapsed time makes it impossible to distinguish among protracted, arrested, and failed descent, each of which has a different prognosis for the labor ending in a safe vaginal delivery.10 Moreover, there is evidence that morbidity associated with a very long second stage is largely confined to those with abnormal descent patterns.87 If this is confirmed, the approach recommended by the new guidelines
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ajog.org will result in increased maternal and neonatal morbidity. The studies that purport to show that the traditional second-stage labor data are incorrect demonstrate a similar pattern of descent to that described by Friedman, but the lower limits of normal are slower, about 0.5 cm/h for nulliparas.11,88 The new guidelines indicate that an “arrest of labor in the second stage” can be diagnosed only after a nullipara has been pushing for at least 3 hours and a multipara for 2 hours. If epidural anesthesia is used, an additional hour is permissible, but then only as long as progress is being documented. Otherwise stated, 3 hours of maternal bearing-down efforts with no progress in descent are acceptable. We are concerned that this practice may expose the fetus to harm from excessive head compression. A recent influential report4 further indicated that no progress in rotation during these time periods also constitutes an arrest of labor in the second stage. The proposal that lack of rotation, independent of descent, should be used as a diagnostic criterion is heterodox and has not been substantiated. Rotation in the second stage cannot occur without descent, and a normal second stage can occur without rotation. (For example, an occiput posterior-positioned fetus descending in an anthropoid pelvis may never rotate, and yet descend at a normal rate.) Therefore, we urge that the presence or absence of rotation not be used for the diagnosis of descent disorders. There is no doubt that epidural anesthesia can lengthen the second stage, probably by inhibiting the mother’s ability to push or by relaxing pelvic floor musculature. The degree of inhibition may be minimal or considerable. It varies among patients, and probably depends, among many factors, on the type and dose of analgesic and anesthetic agents used. It is, therefore, reasonable to consider epidural anesthesia as a cause of or contributor to a descent disorder. Its inhibitory effects can generally be overcome with oxytocin; but it is wise to remember that the presence of an epidural block does not mean other, potentially insurmountable, causes of abnormal descent are absent. Ignoring
that fact and depending solely on duration of pushing risks making labors unnecessarily long and adds risk. A recent study of the effects of epidural medication suggested that the inhibition of labor progress might be considerably greater than has been assumed.89 Whether that observation is generalizable remains to be seen, but it underlines the fact that using duration as the sole indicator of second-stage progress can lead the practitioner astray. We have long opposed the American tradition of limiting the second stage to 2 hours, and of encouraging intense and sustained pushing with each contraction, which may not always be in the best interests of fetus or mother.19,23,90 Most, but not all, studies of the effect of second-stage length found little effect of duration per se on early neonatal outcome for second stages up to at least 3 hours,90-92 but there is little information on long-term maternal or neonatal morbidity. Maternal infection and hemorrhage risk does tend to increase after very long second-stage labors, due in part to the associated high likelihood of cesarean or operative vaginal delivery. Unfortunately, most studies of the effect of second-stage labor duration have not stratified cases according to whether the rate of descent was normal, and this may be a relevant factor.87 The consequences of the very long second stages advocated in the new guidelines could be detrimental, especially when there is no descent of the fetal head. Absent more information about the consequences of such labors for the maternal pelvic floor or for the fetus exposed to enormous intracranial pressures sufficient to impair brain blood flow,67,68,93 the new recommendations seem, at best, incautious. Take as an example the case of a fetus in an occiput posterior position and marked cranial molding at the onset of the second stage, and with the leading surface of the head at the level of the ischial spines in a funnel pelvis. The suggestion that the mother should remain in the second stage pushing for 3 hours before intervention, even without any progress in descent, seems to us to invite peril. The new guidelines also
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recommend manual rotation of the fetal head in cases of malposition to avoid cesarean delivery. We agree that manual rotation (which requires skill and experience to perform safely) can sometimes be a useful tool. However, the recommendation that manual rotation be employed without careful assessment of the pelvis is not responsible. Do we really want to rotate an occiput posterior fetus to an anterior position in an anthropoid pelvis with prominent ischial spines, narrow forepelvis, and a deep sacral hollow? If such a fetus were to deliver vaginally, would it not do so more safely and easily in a posterior position, rather than being forced to accommodate to a pelvis less well suited to its further descent?
Implementation It is simplistic and wrong to expect that any labor curve abnormality will necessarily signal that cesarean delivery is required. The clinical evaluation of labor is essentially a process of serially estimating the likelihood of a safe vaginal delivery.23 Graphic labor patterns are an excellent tool for that purpose, but they should never be used in isolation, because many other factors contribute to the probability of safe delivery. These include the degree of cranial molding, head position and attitude, and the bony architecture of the pelvis, all of which can be determined clinically. In addition, the response to oxytocin, the fetal heart rate pattern, and factors such as fetal weight and sex, maternal body mass, and the presence of infection are important in this regard. The average parturient in today’s industrialized world is older, more obese, and more likely to have epidural anesthesia, induced labor, and a larger baby than in generations past. That these factors may make dysfunctional labor more common is valuable information for the clinician, and should help guide decision-making, but should not necessarily result in more cesarean deliveries for dystocia. A labor disorder merely tells us something about the labor that should prompt extra scrutiny and reasoned analysis.
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Arguably, the most important virtue of the approach to labor we have encouraged is not in the numerical details of the curves, but in the way they can inform a logical and safe system of care during labor and delivery. We have advocated a method that allows a systematic measure of labor progress, provides an unequivocal language for communication about it, and encompasses a consistent and logical guide to decision-making.23 Furthermore, information derived from the curves has revealed clues to the risks inherent in certain aspects of labor and delivery.23,62,80,82-85 In aiming to restructure our fundamental understanding of normal labor progress, the guidelines raise a more general question about the incorporation of new research findings into practice. New observations are generally slow to enter professional guidelines and even slower to become common practice. This restraint allows new approaches to be confirmed by further study. Considering the conservative nature of that process, should we uncritically accept the recommended paradigm shift in labor management at this time, or should we await further confirmation of its value? We urge a cautious and considered approach. Adoption of uncorroborated new practices can have all sorts of unanticipated consequences, including harm to patients.
Conclusions The stated goal of the ACOG/SMFM Guidelines is to provide safe clinical strategies to prevent primary cesarean delivery. Whether the recommendations will achieve widespread acceptance remains to be seen. Our specialty has previously attempted to curtail the rising cesarean rate. Although success has been achieved in some individual institutions,94,95 the rising overall rate has not been significantly affected by the introduction of new guidelines. The recommendations of a national consensus conference on cesarean delivery in 198196 were, for example, largely ineffective. This is not surprising, given the difficulty of changing established practice in most areas of medicine.97-99
ajog.org Perhaps the pursuit of a desirable cesarean delivery rate will not bring us down the most worthy or productive path. The current cesarean rate is merely a symptom of a multifaceted and poorly understood process. Treating symptoms is rarely as satisfactory as is modifying or eliminating their source. If we direct our clinical and basic science investigations to the goal of practicing obstetrics in a manner that optimizes maternal and newborn outcomes, the ideal cesarean delivery rate, whatever it may be, will follow. The use of new databases, prospective designs, and new statistical methods to reassess data derived many years ago is quite reasonable. Novel findings deserve our respect and invite constructive scrutiny. Our overriding concern about the ACOG/SMFM recommendations is that they do not offer an encompassing paradigm for management. Friedman provided a nosology for dysfunctional labor, and, based on it, a system of care that is logical, reproducible, and easily applied. Failure to apply principles correctly can lead to specious diagnoses as well as untimely and inappropriate intervention.86 To adopt sweeping new guidelines for the assessment of labor that largely ignore antecedent obstetric practice is premature. One could infer from them that cultivation of the physical diagnostic skills necessary to become an astute obstetrician is no longer important. The guidelines never mention the need for measurement of fetal station, understanding the implications of the mechanism of labor, or any aspect of clinical cephalopelvimetry. They encourage considerably longer labors in first and second stage than generally practiced today, but they provide no evidence that such lengths would be safe for mother or baby. In fact, the guidelines regarding management of arrest disorders ignore the potential for any maternal or fetal risk. We do not know nearly enough about the association of long labor with chorioamnionitis, neonatal ischemic encephalopathy, birth injury, and maternal pelvic floor injury to abide the extended labors recommended by the guidelines.
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While the goals of the ACOG/SMFM Guidelines are admirable, their recommendations for the assessment of labor depart substantially from accepted norms, and no data yet exist to support the superiority or even the equivalence of the proposed paradigm for labor assessment and management to that which has served our patients well for many decades. Absent such data, It seems unwise to jettison 50 years of corroborated work with what Sir Robert Hutchison100 referred to as “too much zeal for the new and contempt for what is old.” Perhaps we should temper our enthusiasm and seek to verify what really constitutes best practice. The last thing anyone wants is for a new system to do a disservice to the women and babies entrusted to our care. REFERENCES 1. Millen KR, Kuo K, Zhao L, Gecsi K. Evidencebased guidelines in labor management. Obstet Gynecol Surv 2014;69:209-17. 2. Cahill AG, Tuuli MG. Labor in 2013: the new frontier. Am J Obstet Gynecol 2013;209:531-4. 3. El-Sayed YY. Diagnosis and management of arrest disorders: duration to wait. Semin Perinatol 2012;36:374-8. 4. Spong CY, Berghella V, Wenstrom KD, Mercer BM, Saade GR. Preventing the first cesarean delivery: summary of a joint Eunice Kennedy Shriver National Institute of Child Health and Human Development, Society for Maternal-Fetal Medicine, and American College of Obstetricians and Gynecologists Workshop. Obstet Gynecol 2012;120:1181-93. 5. American College of Obstetricians and Gynecologists; Society for Maternal-Fetal Medicine. Safe prevention of the primary cesarean delivery. Obstetric care consensus no. 1. Obstet Gynecol 2014;123:693-711. 6. Friedman EA. The graphic analysis of labor. Am J Obstet Gynecol 1954;68:1568-75. 7. Friedman EA. Primigravid labor: a graphicostatistical analysis. Obstet Gynecol 1955;6: 567-89. 8. Friedman EA. Labor in multiparas: a graphicostatistical analysis. Obstet Gynecol 1956;8: 691-703. 9. Friedman EA. Labor: clinical evaluation and management. New York: Appleton-CenturyCrofts; 1967. 10. Friedman EA. Labor: clinical evaluation and management, 2nd ed. New York: AppletonCentury-Crofts; 1978. 11. Zhang J, Troendle JF, Yancey MK. Reassessing the labor curve in nulliparous women. Am J Obstet Gynecol 2002;187:824-8. 12. Zhang J, Troendle J, Mikolajczyk R, Sundaram R, Beaver J, Fraser W. The natural
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ajog.org history of the normal first stage of labor. Obstet Gynecol 2010;115:705-10. 13. Zhang J, Landy HJ, Branch DW, et al. Contemporary patterns of spontaneous labor with normal neonatal outcome. Obstet Gynecol 2010;116:1281-7. 14. Laughon SK, Branch DW, Beaver J, Zhang J. Changes in labor patterns over 50 years. Am J Obstet Gynecol 2012;206:419.e1-9. 15. Williams JW. Obstetrics: a text-book for the use of students and practitioners. New York: D. Appleton and Co; 1903. 16. Wolf W. Der unzeitige Blasensprung. Stuttgart: Wissenschaftliche Verlagsgesellschaft; 1946. p.103. 17. Koller T. Versuch einer graphischen Darstellung des Geburtsverlaufes. Gynaecologia 1948;126:227. 18. Zimmer K. Die Muttermundseröffnung bei den Schädellagen im Wegzeit-Diagramm. Arch Gynaekol 1951;179:495-513. 19. Cohen WR, Acker DB, Friedman EA, eds. Management of labor, 2nd ed. Rockville, MD: Aspen Publishers Inc; 1989. 20. Cohen WR. Normal and abnormal labor. In: Reece EA, Hobbins J, eds. Clinical obstetrics: the fetus and mother, 3rd ed. London: Blackwell Publishing Ltd; 2007:1065-76. 21. Cohen WR, Friedman EA. The assessment of labor. In: Kurjak A, Chervenak FA, eds. Textbook of perinatal medicine, 2nd ed. London: Informa; 2006:1821-30. 22. Cohen WR. Controversies in the assessment of labor. Prog Obstet Gynecol 2006;17: 231-44. 23. Cohen WR, Friedman EA. Labor and delivery care: a practical guide. Oxford: John Wiley and Sons Ltd; 2011. 24. Bottoms SF, Hirsch VJ, Sokol RJ. Medical management of arrest disorders of labor: a current overview. Am J Obstet Gynecol 1987;156:935-9. 25. Sokol RJ, Stojkov J, Chik L, Rosen MG. Normal and abnormal labor progress, I: a quantitative assessment and survey of the literature. J Reprod Med 1977;18:47-53. 26. Duignan NM, Studd JWW, Hughes AO. Characteristics of normal labor in different racial groups. Br J Obstet Gynecol 1975;82:593-601. 27. Hendricks CH, Brenner WE, Kraus G. Normal cervical dilatation pattern in late pregnancy and labor. Am J Obstet Gynecol 1970;106:1065-82. 28. Ledger WJ. Monitoring of labor by graphs. Obstet Gynecol 1969;34:174-81. 29. Ledger WJ, Witting WC. The use of a cervical dilatation graph in the management of primigravidae in labor. 1972;79:710-4. 30. Evans MI, Lachman E, Kral S, Melmed H. Predictive value of cervical dilatation rates in labor in multiparous women. Isr J Med Sci 1976;12:1399-403. 31. Melmed H, Evans M. Predictive value of cervical dilatation rates, I: primipara labor. Obstet Gynecol 1976;47:511-5. 32. Kwast BE, Lennox CE, Farley TMM. World Health Organization partograph in management of labor. Lancet 1994;343:1399-404.
33. Poma PA. Use of labor graphs in a community hospital. Int Surg 1979;64:7-12. 34. Studd J, Clegg DR, Sanders RR, Hughes AO. Identification of high risk labors by labor nomogram. Br Med J 1975;2:545-7. 35. Philpott RH, Castle WM. Cervicographs in the management of labor in primigravidae. J Obstet Gynaecol Br Commonw 1972;79: 599-602. 36. Van Bogaert L-J. The partogram’s result and neonatal outcome. J Obstet Gynaecol 2006;26:321-4. 37. Drouin P, Nkounawa F. The value of the partogram in the management of labor. Obstet Gynecol 1979;53:741-5. 38. Cibils LA, Hendricks CH. Normal labor in vertex presentation. Am J Obstet Gynecol 1965;91:385-95. 39. Juntunen J, Kirkinen P. Partogram of a grand multipara: different descent slope compared with an ordinary parturient. J Perinat Med 1994;22:213-8. 40. Lekprasert V. Monitoring of labor by graph. J Med Assoc Thai 1972;55:647-53. 41. Peisner DB, Rosen MG. Transition from latent to active labor. Obstet Gynecol 1986;68: 448-51. 42. Duncan GR, Costello E. The partogram: a graphic guide to progress in labor. N Z Med J 1975;82:193-5. 43. Incerti M, Locatelli A, Ghidini A, Ciriello E, Consonni S, Pezzullo JC. Variability in rate of cervical dilatation in nulliparous women at term. Birth 2011;38:30-5. 44. Friedman EA. Cervimetry: an objective method for the study of cervical dilatation in labor. Am J Obstet Gynecol 1956;71:1189-93. 45. Friedman EA, Von Micsky LI. Electronic cervimeter: a research instrument for the study of cervical dilatation in labor. Am J Obstet Gynecol 1963;87:789-93. 46. Zador I, Neuman MR, Wolfson RN. Continuous monitoring of cervical dilatation during labor by ultrasonic transit time measurement. Med Biol Eng 1976;14:299-305. 47. Kok FT, Wallenburg HCS, Wladimiroff JW. Ultrasonic measurement of cervical dilatation during labor. Am J Obstet Gynecol 1976;126: 288-90. 48. Eijskoot F, Storm J, Kok F, Wallenburg H, Wladimiroff J. An ultrasonic device for continuous measurement of cervical dilatation during labor. Ultrasonics 1977;15:183-5. 49. Richardson JA, Sutherland IA, Allen DW. A cervimeter for continuous measurement of cervical dilatation in labor: preliminary results. Br J Obstet Gynaecol 1978;85:178-84. 50. Sharf Y, Farine D, Batzalel M, et al. Continuous monitoring of cervical dilatation and fetal head station during labor. Med Eng Phys 2007;29:61-71. 51. van Dessel HJ, Frijns JH, Kok FT, Wallenburg HC. Ultrasound assessment of cervical dynamics during the first stage of labor. Eur J Obstet Gynecol 1994;53:123-7. 52. Breeveld-Dwarkasing VNA, Struijk PC, Lotgering FK, et al. Cervical dilatation related
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to uterine electromyographic activity and endocrinological changes during prostaglandin F2a-induced parturition in cows. Biol Reprod 2003;68:536-42. 53. Friedman EA, Kroll BH. Computer analysis of labor progression. J Obstet Gynaecol Br Commonw 1969;76:1075-9. 54. Friedman EA, Kroll BH. Computer analysis of labor progression, II: distribution of data and limits of normal. J Reprod Med 1971;6: 43-8. 55. Friedman EA, Kroll BH. Computer analysis of labor progression, III: pattern variations by parity. J Reprod Med 1971;6:179-83. 56. Friedman EA, Kroll BH. Computer analysis of labor progression, IV: diagnosis of secondary arrest of dilatation. J Reprod Med 1971;7:176-8. 57. Bliss CI. The method of probits. Science 1934;79:38-9. 58. Finney DJ. Probit analysis. Cambridge (United Kingdom): Cambridge University Press; 1952. 59. Montgomery DC, Peck EA, Vining GG. Introduction to linear regression analysis, 5th ed. London: John Wiley and Sons; 2012:7.1. 60. Gurewitsch ED, Diament P, Fong J, et al. The labor curve of the grand multipara: does progress of labor continue to improve with additional childbearing? Am J Obstet Gynecol 2002;186:1331-8. 61. Chen HF, Chu KK. Double-lined nomogram of cervical dilatation in Chinese primigravidas. Acta Obstet Gynecol Scand 1986;65:573-5. 62. Friedman EA, Neff RK. Labor and delivery: impact on offspring. Littleton, MA: PSG Publishing; 1987. 63. Vahratian A, Troendle JF, Seiga-Riz AM, Zhang J. Methodological challenges in studying labor progression in contemporary practice. Paediatr Perinat Epidemiol 2006;20:72-8. 64. Rouse DJ, Owen J, Savage KG, Hauth JC. Active phase labor arrest: revisiting the 2-hour minimum. Obstet Gynecol 2001;98:550-4. 65. Rouse DJ, Owen J, Hauth JC. Active phase labor arrest: oxytocin augmentation for at least 4 hours. Obstet Gynecol 1999;93:323-8. 66. Rouse DJ, McCullough C, Wren AL, Owen J, Hauth JC. Active-phase labor arrest: a randomized trial of chorioamnion management. Obstet Gynecol 1994;83:937-40. 67. Schwarcz RL, Strada-Saenz G, Althabe O, Fernandez-Funes J, Alvarez LO, CaldeyroBarcia R. Pressure exerted by uterine contractions on the head of the human fetus during labor. In: World Health Organization. Perinatal factors affecting human development. Washington (DC): Pan American Health Organization; 1969:133-43. 68. Schifrin BS, Deymier P, Cohen WR. Fetal neurological injury related to mechanical forces of labor and delivery. In: Zhang L, ed. Stress and developmental programming in health and disease: beyond phenomenology. Hauppauge, New York: Nova Science Publishers; 2014: 651-88. 69. Bugg GJ, Siddiqui F, Thornton JG. Oxytocin versus no treatment or delayed treatment for
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slow progress in the first stage of spontaneous labor. Cochrane Database Syst Rev 2011: CD007123. 70. Steer PJ, Carter MC, Beard RW. The effect of oxytocin infusion on uterine activity in slow labor. Br J Obstet Gynaecol 1985;92:1120-6. 71. Friedman EA, Sachtleben MR. Dysfunctional labor, II: protracted active-phase dilatation in the nullipara. Obstet Gynecol 1961;17:566-78. 72. Bakker JJ, Janssen PF, van Halem K, et al. Internal versus external tocodynamometry during induced or augmented labor. Cochrane Database Syst Rev 2013;8:CD006947. 73. Bakker JJ, Verhoeven CJ, Janssen PF, et al. Outcomes after internal versus external tocodynamometry for monitoring labor. N Engl J Med 2010;362:306-13. 74. Chua S, Kurup A, Arulkumaran S, Ratnam SS. Augmentation of labor: does internal tocography result in better obstetric outcome than external tocography? Obstet Gynecol 1990;76:164-7. 75. Jacobson JD, Gregerson GN, Dale S, Valenzuela GJ. Real-time microcomputer-based analysis of spontaneous and augmented labor. Obstet Gynecol 1990;76:755-8. 76. Oppenheimer LW, Bland ES, Dabrowski A, Holmes P, McDonald O, Wen SW. Uterine contraction pattern as a predictor of mode of delivery. J Perinatol 2002;22:149-53. 77. Towner D, Castro MA, Eby-Wilkens E, Gilbert WM. Effect of mode of delivery in nulliparous women on neonatal intracranial injury. N Engl J Med 1990;341:1709-14. 78. Friedman EA, Sachtleben MR. Dysfunctional labor, V: therapeutic trial of oxytocin in secondary arrest. Obstet Gynecol 1963;21:13-21. 79. Caldeyro-Barcia R. Adverse perinatal effects of early amniotomy during labor. In: Gluck L, ed. Modern perinatal medicine. Chicago: Year Book Medical Publishers; 1974.
ajog.org 80. Nguyen T, Handa VL, Hueppchen N, Cundiff GW. Labor curve findings associated with fourth degree sphincter disruption: the impact of labor progression on perineal trauma. J Obstet Gynaecol Can 2010;32:21-7. 81. Kushtagi P. Pattern of descent of fetal head in normal labor. J Indian Med Assoc 1995;93: 336-9. 82. Gross T, Sokol RJ, Williams T, Thompson K. Shoulder dystocia: a fetal-physician risk. Am J Obstet Gynecol 1987;156:1408-18. 83. Hopwood HG. Shoulder dystocia: fifteen years’ experience in a community hospital. Am J Obstet Gynecol 1982;144:162-6. 84. Weizsaecker K, Deaver JR, Cohen WR. Labor characteristics and neonatal Erb’s palsy. BJOG 2007;114:1003-9. 85. Deaver JE, Cohen WR. A prediction model for brachial plexus injury. J Perinat Med 2009;37: 150-5. 86. Garrett K, Butler A, Cohen WR. Cesarean delivery during second stage labor: characteristics and diagnostic accuracy. J Matern Fetal Neonatal Med 2005;17:49-53. 87. Cohen WR, Mahon T, Chazotte C. Very long second stage of labor: characteristics and outcome. In: Cosmi EV, ed. Labor and delivery: the proceedings of the second world congress on labor and delivery. New York: Parthenon Publishing Group; 1998:348-51. 88. Graseck A, Tuuli M, Roehl K, Odibo A, Macones G, Cahill A. Fetal descent in labor. Obstet Gynecol 2014;123:521-6. 89. Cheng YW, Shaffer BL, Nicholson JM, Caughey AB. Second stage of labor and epidural use: a larger effect than expected. Obstet Gynecol 2014;123:527-35. 90. Cohen WR. Influence of the duration of second stage labor on perinatal outcome and puerperal morbidity. Obstet Gynecol 1977;49: 266-9.
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91. Laughon SK, Berghella V, Reddy UM, Sundaram R, Lu Z, Hoffman MK. Neonatal and maternal outcomes with prolonged second stage of labor. Obstet Gynecol 2014;124: 57-67. 92. 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 2004;191:933-8. 93. O’Brien WF, Davis SE, Grissom MP, Eng RR, Golden SM. Effect of cephalic pressure on fetal cerebral blood flow. Am J Perinatol 1984;1:223-6. 94. Sanchez-Ramos L, Kaunitz AM, Peterson MD, et al. Reducing cesarean sections at a teaching hospital. Am J Obstet Gynecol 1990;163:1081-8. 95. Meyers SA, Gleicher N. A successful program to lower cesarean rates. N Engl J Med 1988;319:1511-6. 96. National Institutes of Health. Cesarean birth task force development report. Obstet Gynecol 1981;57:537-45. 97. Oppenheimer LW, Holmes P, Yang O, Yang T, Walker M, Wen SW. Adherence to guidelines on the management of dystocia and cesarean section rates. Am J Perinatol 2007;24: 271-6. 98. Grol R, Dalhuijsen J, Thomas S, Veld C, Rutten G, Mokkink H. Attributes of clinical guidelines that influence use of guidelines in general practice: observational study. BMJ 1998;317:858-61. 99. Lomas J, Anderson G, Domnick-Pierre K, Vayda E, Enkin M, Hannah W. Do practice guidelines guide practice? The effect of a consensus statement on the practice of physicians. N Engl J Med 1989;321:1306-11. 100. Hutchison R. The physician’s prayer. BMJ 1998;317:1687.
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OBSTETRICS
Perils of the new labor management guidelines Wayne R. Cohen, MD; Emanuel A. Friedman, Med ScD
T
he seemingly inexorable increase in the use of cesarean delivery, and the substantial contribution that dystocia and related diagnoses have made to that increase, have prompted a reevaluation of what constitutes normal labor.1-4 As a result, new guidelines promulgated jointly by the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) were released.5 The new recommendations define abnormal labor and provide guidelines for its management that differ sharply from those originally described by Friedman,6-10 which have formed the basis of the clinical management of labor for many decades in the United States and elsewhere. For that reason, a thorough analysis of the proposed standards is warranted to ensure that changes recommended for obstetric care during labor are justified by the available evidence. The guidelines are based heavily on analytic methods used by Zhang and colleagues11-14 to describe the patterns of cervical dilatation and fetal descent as functions of time elapsed in labor. Their findings, which have been rapidly adopted in some parts the obstetric community, have not yet been validated. For the reasons we briefly summarize in this commentary, we believe the new ACOG/SMFM recommendations From the Department of Obstetrics and Gynecology, University of Arizona College of Medicine, Tucson, AZ (Dr Cohen); and the Department of Obstetrics, Gynecology, and Reproductive Biology, Harvard Medical School, Boston, MA (Dr Friedman). Received Aug. 11, 2014; revised Aug. 20, 2014; accepted Sept. 2, 2014. The authors report no conflict of interest. Corresponding author: Wayne R. Cohen, MD. [email protected] 0002-9378/$36.00 ª 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.ajog.2014.09.008
Recent guidelines issued jointly by the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine for assessing labor progress differ substantially from those described initially by Friedman, which have guided clinical practice for decades. The guidelines are based on results obtained from new and untested methods of analyzing patterns of cervical dilatation and fetal descent. Before these new guidelines are adopted into clinical practice, the results obtained by these unconventional analytic approaches should be validated and shown to be superior, or at least equivalent, to currently accepted standards. The new guidelines indicate the patterns of labor originally described by Friedman are incorrect and, further, are inapplicable to modern obstetric practice. We contend that the original descriptions of normal and abnormal labor progress, which were based on direct clinical observations, accurately describe progress in dilatation and descent, and that the differences reported more recently are likely attributable to patient selection and the potential inaccuracy of very high-order polynomial curve-fitting methods. The clinical evaluation of labor is a process of serially estimating the likelihood of a safe vaginal delivery. Because many factors contribute to that likelihood, such as cranial molding, head position and attitude, and the bony architecture and capacity of the pelvis, graphic labor patterns should never be used in isolation. The new guidelines are based heavily on unvalidated notions of labor progress and ignore clinical parameters that should remain cornerstones of intrapartum decision-making. Key words: active phase, arrest of descent, arrest of dilatation, arrest of labor, deceleration phase, dysfunctional labor, labor curve, partogram
provide definitions of dysfunctional labor and guidelines for its management that, however well intentioned, are likely to impose undue risk on mother and fetus.
Historical background Prior to the mid-1950s, the evaluation of progress in labor was based primarily on its duration. Vague admonitions such as, “Never let the sun set twice on a laboring woman,” which were based on prevailing observations about average labor duration and outcomes,15 were commonly intoned. This approach was, however, ineffective in identifying when intervention would be appropriate or optimal. In 1954, the first of hundreds of studies of labor by, or based on the work of, Emanuel Friedman6 was published. Friedman’s work built upon previous investigators’ attempts to describe the events of labor as a function of
time.16-18 Their recognition of the practical implications of this approach was hampered by what we now know to have been erroneous assumptions about labor, particularly with regard to the role of membrane rupture. The first publications6-8 describing the graphic patterns of dilatation and descent stimulated the interest of many investigators, and led to the formulation of criteria that made the assessment of progress in labor objective rather than arbitrary.9,10,19-26 Unfortunately, the criteria have not always been applied appropriately, in part because of some misunderstandings about the curves and their proper place in clinical care.
Misconceptions It has often been alleged that Friedman’s seminal observations regarding the labor curves rest on a fragile foundation because they were never corroborated by others. In fact, numerous studies done
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in different parts of the world over the course of several decades confirmed the basic nature of the original curves, and validated their usefulness in clinical practice.27-43 There have been disagreements over the importance of the latent phase or even the existence of the deceleration phase of dilatation, but the core finding that active-phase cervical dilatation progresses linearly, with a lower limit of normal approximately 1.0 cm/h in nulliparas, has been remarkably consistent among studies. It is also noteworthy that in many institutions the introduction of labor curves to clinical care was associated with a decline in the cesarean rate.30,33,34 Some of the early data were collected using a mechanical cervimeter to obviate the potential subjectivity in clinical examination,9,44,45 and cervimetry by investigators using various tools confirmed the sigmoid nature of the dilatation curve.46-49 Limited data from more recently developed techniques to automate cervical assessment also appear consistent with the earlier observations.50,51 Sigmoid-shaped curves of cervical dilatation have even been described in cows, suggesting a common pattern of labor among mammalian species.52 Given the large body of evidence confirming the basic pattern of progress in normal labor, it is difficult to believe that labor progresses very differently today from how it was originally described. Why, then, do the labor curves of Zhang and his colleagues differ from those of previous observers? One explanation was provided by Zhang himself when he and his colleagues applied their analytical methods to the very same data Friedman had analyzed from the Collaborative Perinatal Project.14 Friedman’s analysis of those data revealed a sigmoid-shaped dilatation curve; that of Zhang et al revealed an exponential curve, essentially the same as they had found from contemporary labors. Clearly, what had changed was not the nature of progress in labor, but how the data were analyzed. This raises the question of which analytic technique provides a more accurate model of labor progress: that of Friedman or that of Zhang et al?
ajog.org In trying to address that question it is important to understand that the original dilatation and descent curves were based on and confirmed by direct experimental observations made on women in labor. The primacy of direct observation over theoretical conceptualization or indirect analysis of data in hypothesis testing has been a central tenet of the scientific method since the Enlightenment. When the results of an analytic approach differ from those derived from observation, it is important to understand why this has occurred, and try to adjudicate accordingly, before declaring the direct objective findings invalid. Analytical issues The labor curves in Friedman’s original reports were not created by using complex mathematical formulae, as some have suggested.2 The initial data were collected by a single observer.6 Subsequently, data from multiple practitioners in a single institution were reported.7,8 In both instances, the curves were drawn by hand, the descriptions were empiric, and the statistical analysis basic. Only later was a more sophisticated method of assessing the labor graphs by computer used to analyze >10,000 nulliparas from multiple institutions.53-56 This more sophisticated analysis confirmed the initial findings regarding the nature of the cervical dilatation and head descent time functions. The computer algorithm used was developed with the Office of Biometry of the National Institutes of Health. Raw labor data were plotted on a probit (ie, the normal probability) scale, to convert the sigmoid curves to straight lines.57,58 The maximum slope data were converted to logarithms to normalize their right-skewed distribution. The linearity thus achieved made the data amenable to descriptive statistical study for determining distributions and limits of normal, which have until recently stood the tests of time and clinical applicability. By contrast, Zhang and colleagues used a high-order polynomial curvefitting program to analyze dilatation and descent data, and interval-censored
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regression to fit curves based on centimeter-by-centimeter median traverse times. We have concerns about the application of this technique to labor. We do not profess personal expertise in this area, but we are impressed by the negative comments and strong skepticism encountered in the engineering literature pertaining to the limitations of high-order curve-fitting methods.59 Such models do not guarantee reliable results. Indeed, high-order curve fitting may not be appropriate or even necessary for most situations. Low-order quadratic curve fitting is preferable, whenever possible, and yields results that are at least as accurate. In fact, the higher the order, the less satisfactory curvefitting accuracy tends to be. This is so because ‘noise’ (ie, unstable data points, especially if those points are spread apart from each other or are located at the ends of the range of data) is magnified. As a consequence, portions of the derived curve are distorted. In this regard a leading authority opined that, “It is important to keep the order of the model as low as possible.As a general rule the use of high-order polynomials (k >2) should be avoided unless they can be justified for reasons outside the data.Arbitrary fitting of high-order polynomials is a serious abuse of regression analysis.”59 Zhang et al used polynomial curve-fitting models of the order of 810, far in excess of the cited recommendation of no higher than 1 or 2. Other investigators have used interval data to create labor curves, with varying results. Gurewitsch et al60 found a sigmoid curve of dilatation, but Chen and Chu61 found results similar to those of Zhang et al in terms of curve shape and much lower rates of dilatation. Thus, the differences alleged to exist between the Friedman and the Zhang curves are likely due to the different mathematical models used to fit these curves. This is confirmed by Zhang’s finding, noted above, that the same data Friedman and Neff62 analyzed decades ago yielded exponential curves with the curve-fitting methods used by Zhang and his colleagues.14 The approach by Zhang et al is likely to have introduced an important set of
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ajog.org selection biases, which also cast doubt on the validity of their findings. Women with rapidly progressing labors tend to present themselves for obstetric care and be first examined at more advanced cervical dilatation than those with longer labor. Thus, the intervals at the distal end of the dilatation curve are likely to have been loaded with progressively more rapid labors. This may explain the exponential nature of the dilatation curve derived in this manner. It may also explain why the descent curve, which was unencumbered by that problem because all patients were present and under observation for their entire second stage, looks very much like that originally reported.11 In addition, the labor curves of Zhang et al were generated after excluding women delivered by cesarean. Many of these were undoubtedly having slow, dysfunctional labor patterns that led to a diagnosis of dystocia and the need for cesarean delivery. Their exclusion is likely, therefore, to have falsely increased the average rate of dilatation in residual study cases, contributing to the exponential appearance of the curves. Zhang et al also excluded women whose cervix was >6 cm dilated at admission, probably thus excluding many of the most rapid labors and contributing to the overall appearance of slow average dilatation. In fact, these and other biases were acknowledged by Zhang and his colleagues.63 They stated that the fact that their study excluded first-stage cesareans “limit[ed] the generalizability of the results.” They also acknowledged the probable disparity in dilatation rates among parturients admitted at different time points in labor, thus raising doubts about the comparability of data derived from these sequential points. They further reported that their labor curves “are unadjusted for potential confounders, such as oxytocin use. While it is technically possible to control for confounders.it complicates the interpretation of the results..” They also acknowledged that “.time intervals for more advanced cervical dilation were affected to an extent by dropout of women because of caesarean delivery for
labor arrest. Such dropouts usually are not random. Slow progressing labors often dropped out early, making the average time intervals for the remaining women appear shorter than otherwise. The degree of bias depends on the incidence of first-stage caesarean delivery. Unfortunately, we have not yet recognized an easy solution to overcome this informed censoring.” To summarize, Zhang and colleagues have themselves acknowledged that both the selection biases and the unadjusted confounders likely influenced the shape of their dilatation curve either by slowing the early aspects of the active phase (or the transition from latent to active phase) or speeding the late aspects of the active phase, or both. The combined effect of these biases probably explains in part their finding that the rate of active-phase dilatation increases exponentially, rather than linearly as Friedman and many others have previously found.6-10,25-31,35-46 Transition to active phase One critically important way in which the new guidelines depart from the old is in identifying the transition from latent to active phase during the first stage. It is widely, but erroneously, concluded from the Friedman dilatation curve that the active phase of labor begins at 4 cm. Some studies have even used 3 cm as the definition of entry into active phase.64-66 According to the guidelines, the active phase begins at 6 cm. The difference is of critical importance, because it has a dramatic effect on whether dysfunctional labor can be diagnosed early in the active phase. Important labor abnormalities (protracted active phase and arrest of dilatation) that would be identified by the Friedman curve prior to 6 cm of dilatation would be classified as normal by the new guidelines. Why the active phase of first-stage labor has been inferred to begin at 4 cm is puzzling. We, in fact, have never suggested that the active phase begins at either 4 or 3 cm of cervical dilatation; on the contrary, we have expressly discouraged the use of any specific degree of dilatation for the identification of the
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active phase.23 Observations of dilatation data make it clear the active phase can begin anywhere from 3-6 cm, and, occasionally, earlier or later, depending on the individual labor.23,41 Using an arbitrary cutoff sacrifices accuracy for ease, and this unnecessary oversimplification risks incorrect diagnosis. The transition from the latent phase to the active phase can be correctly identified only by interpretation of serial clinical examinations for each patient as her labor progresses. Consider, for example, a labor that begins with the cervix 2 cm dilated for several hours. It then dilates rapidly to 5 cm in 1 hour, but fails to dilate further over the next 2 hours. According to the new guidelines, that would be normal latent-phase labor. To us it is an arrest of dilatation in active-phase labor that requires thorough evaluation to search for a cause. The likelihood that it will resolve itself (as many arrest disorders do) or would benefit from oxytocin stimulation would depend on the clinical circumstances, determinable by evaluation of mother and fetus. If there were significant molding and a narrow pelvis, little would be gained by further labor, and the fetus might be exposed to unnecessary risk.67,68
Diagnosis of arrest of dilatation Under the new guidelines, neither protracted active phase nor arrest of dilatation should be diagnosed in a nullipara before 6 cm cervical dilatation, and the lower limit of normal active-phase dilatation is about 0.5 cm/h, rather than the 1.0 or 1.2 cm/h reported by Friedman and others. The guidelines do recognize that there can be slow but progressive first-stage dilatation (protracted active phase), and that it should not be an indication for cesarean delivery, but they conflate protracted active phase and arrest of dilatation, despite evidence that they may be distinct disorders that respond differently to therapy and have a different prognosis.10,23 A protracted active phase, unless it has been caused by factors that inhibit contractility, such as anesthesia, infection, and (possibly) obesity, does not respond to oxytocin stimulation with an increased rate of
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dilatation. Contractility does, however, increase, thus conferring risk with no offsetting benefit.69-71 Role of contractile force To diagnose arrest of dilatation, the guidelines require that the cervix be 6 cm dilated, the membranes be ruptured, and there be no progress for 4 hours with adequate contractions, or 6 hours with inadequate contractions produced by oxytocin. They define adequate uterine contractility as “e.g., >200 Montevideo Units” (MVU), but recommend no alternative means of assessment. Moreover, no upper boundary of MVU is provided, thus condoning the potential exposure of the fetus to excessive uterine contractility. The definition also implies that an internal uterine pressure transducer (IUPT) is useful to diagnose an arrest of dilatation, but this is questionable. The use of MVUs is problematic for several reasons. Intrauterine catheters carry risk, and there is not evidence for benefit. Studies have demonstrated that the use of IUPTs had no advantage when compared to noninvasive means of assessing uterine contractility during labor.72-74 In addition, IUPT readings may depend on patient position, or on their location within the uterus and, most importantly, they do not correlate well with progress in cervical dilatation70,75 or with the need for cesarean delivery.69 Normal progress in dilatation is achieved over a broad range of uterine activity, and the pattern of contractions may be as important as their strength.76 The definition of arrest of dilatation proposed by the guidelines would, for example, allow a labor arrested at 8 cm with strong contractions to continue for at least 4 hours (and an additional 4 hours if the membranes were not ruptured until after the first 4 hours) at that dilatation before an arrest could be diagnosed and the recommended 4 hours of treatment begun. This recommendation would be inadvisable in many circumstances, because it fails to consider any preceding labor abnormalities, the results of clinical cephalopelvimetry, the presence of infection, and other factors that might be
ajog.org contributing to the dysfunction, some of which might not be surmountable. Of even more concern, the recommendations in the guidelines implicitly deny the possibility that the fetus could be put at risk by prolonged exposure to strong uterine contractions during an arrest of labor.67,68,77
Treatment of arrest of dilatation We have always taught, based on objective findings, that arrest of dilatation should generally be treated with oxytocin infusion unless there is compelling clinical evidence of disproportion or another contraindication to oxytocin use.23 Although the duration of oxytocin treatment should be tailored to the individual situation, a trial of about 4 hours was recommended as early as 1963.9,78 This approach was confirmed as appropriate more recently by other investigators.65 Several analyses of arrest of dilatation made it clear that the disorder will sometimes resolve spontaneously, but that oxytocin stimulation is often necessary, and usually effective.10,24,78 When oxytocin is used, about 90% of labors that will respond with further dilatation will have done so after 3-4 hours; 7 hours may be necessary before all cases have responded. Rupture of membranes seems to be effective in provoking further sustained dilatation in only a small proportion of cases.10,66 Given the risks associated with rupture of membranes (infection, abnormal fetal heart rate patterns, increased head compression66,68,79) we do not recommend amniotomy as a treatment for arrest disorders, but it should be used if there are other potential benefits, such as better quality fetal heart rate monitoring or more effective clinical evaluation. The deceleration phase During the terminal portion of the active phase of labor (the deceleration phase), uterine contractions remain strong, and the patient may perceive pain of increasing intensity. The graphic appearance of dilatation at this time, however, seems to slow. This results from the cervix being retracted in a
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cephalad direction (relative to the mother) around and alongside the fetal head. As it nears full dilatation, the cervix is no longer opening in a primarily transverse plane relative to the mother’s pelvis. Because our examination only measures dilatation accurately in that plane, dilatation appears to decelerate, even though the cervical rim is still being retracted at about the same speed as before. The deceleration phase is often quite short in normal labors and is easily missed if examinations are not done with sufficient frequency to identify it. The labor patterns reported by Zhang et al11,12 failed to show a deceleration phase, but they did acknowledge that it was present in cases delivered by cesarean that they had excluded from their analysis. In other words, its absence in their average curves was a consequence of patient selection. They excluded the very labors most likely to manifest prolonged deceleration. The presence of the deceleration phase has been confirmed by others.43,49,60,80-83 Despite the artificial nature of the deceleration phase of the dilatation curve, it reflects a critically important time in labor. Deceleration generally marks the beginning of fetal descent, and its prolongation portends significant problems for the labor. Frequent careful examinations during this portion of labor can yield important prognostic insights regarding the risk of shoulder dystocia, abnormal secondstage descent, and the likelihood of the need for cesarean delivery.82-86
The second stage The new guidelines define normal limits for the second stage by elapsed time after full cervical dilatation, and take no account of the rate of fetal descent. Using only elapsed time makes it impossible to distinguish among protracted, arrested, and failed descent, each of which has a different prognosis for the labor ending in a safe vaginal delivery.10 Moreover, there is evidence that morbidity associated with a very long second stage is largely confined to those with abnormal descent patterns.87 If this is confirmed, the approach recommended by the new guidelines
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ajog.org will result in increased maternal and neonatal morbidity. The studies that purport to show that the traditional second-stage labor data are incorrect demonstrate a similar pattern of descent to that described by Friedman, but the lower limits of normal are slower, about 0.5 cm/h for nulliparas.11,88 The new guidelines indicate that an “arrest of labor in the second stage” can be diagnosed only after a nullipara has been pushing for at least 3 hours and a multipara for 2 hours. If epidural anesthesia is used, an additional hour is permissible, but then only as long as progress is being documented. Otherwise stated, 3 hours of maternal bearing-down efforts with no progress in descent are acceptable. We are concerned that this practice may expose the fetus to harm from excessive head compression. A recent influential report4 further indicated that no progress in rotation during these time periods also constitutes an arrest of labor in the second stage. The proposal that lack of rotation, independent of descent, should be used as a diagnostic criterion is heterodox and has not been substantiated. Rotation in the second stage cannot occur without descent, and a normal second stage can occur without rotation. (For example, an occiput posterior-positioned fetus descending in an anthropoid pelvis may never rotate, and yet descend at a normal rate.) Therefore, we urge that the presence or absence of rotation not be used for the diagnosis of descent disorders. There is no doubt that epidural anesthesia can lengthen the second stage, probably by inhibiting the mother’s ability to push or by relaxing pelvic floor musculature. The degree of inhibition may be minimal or considerable. It varies among patients, and probably depends, among many factors, on the type and dose of analgesic and anesthetic agents used. It is, therefore, reasonable to consider epidural anesthesia as a cause of or contributor to a descent disorder. Its inhibitory effects can generally be overcome with oxytocin; but it is wise to remember that the presence of an epidural block does not mean other, potentially insurmountable, causes of abnormal descent are absent. Ignoring
that fact and depending solely on duration of pushing risks making labors unnecessarily long and adds risk. A recent study of the effects of epidural medication suggested that the inhibition of labor progress might be considerably greater than has been assumed.89 Whether that observation is generalizable remains to be seen, but it underlines the fact that using duration as the sole indicator of second-stage progress can lead the practitioner astray. We have long opposed the American tradition of limiting the second stage to 2 hours, and of encouraging intense and sustained pushing with each contraction, which may not always be in the best interests of fetus or mother.19,23,90 Most, but not all, studies of the effect of second-stage length found little effect of duration per se on early neonatal outcome for second stages up to at least 3 hours,90-92 but there is little information on long-term maternal or neonatal morbidity. Maternal infection and hemorrhage risk does tend to increase after very long second-stage labors, due in part to the associated high likelihood of cesarean or operative vaginal delivery. Unfortunately, most studies of the effect of second-stage labor duration have not stratified cases according to whether the rate of descent was normal, and this may be a relevant factor.87 The consequences of the very long second stages advocated in the new guidelines could be detrimental, especially when there is no descent of the fetal head. Absent more information about the consequences of such labors for the maternal pelvic floor or for the fetus exposed to enormous intracranial pressures sufficient to impair brain blood flow,67,68,93 the new recommendations seem, at best, incautious. Take as an example the case of a fetus in an occiput posterior position and marked cranial molding at the onset of the second stage, and with the leading surface of the head at the level of the ischial spines in a funnel pelvis. The suggestion that the mother should remain in the second stage pushing for 3 hours before intervention, even without any progress in descent, seems to us to invite peril. The new guidelines also
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recommend manual rotation of the fetal head in cases of malposition to avoid cesarean delivery. We agree that manual rotation (which requires skill and experience to perform safely) can sometimes be a useful tool. However, the recommendation that manual rotation be employed without careful assessment of the pelvis is not responsible. Do we really want to rotate an occiput posterior fetus to an anterior position in an anthropoid pelvis with prominent ischial spines, narrow forepelvis, and a deep sacral hollow? If such a fetus were to deliver vaginally, would it not do so more safely and easily in a posterior position, rather than being forced to accommodate to a pelvis less well suited to its further descent?
Implementation It is simplistic and wrong to expect that any labor curve abnormality will necessarily signal that cesarean delivery is required. The clinical evaluation of labor is essentially a process of serially estimating the likelihood of a safe vaginal delivery.23 Graphic labor patterns are an excellent tool for that purpose, but they should never be used in isolation, because many other factors contribute to the probability of safe delivery. These include the degree of cranial molding, head position and attitude, and the bony architecture of the pelvis, all of which can be determined clinically. In addition, the response to oxytocin, the fetal heart rate pattern, and factors such as fetal weight and sex, maternal body mass, and the presence of infection are important in this regard. The average parturient in today’s industrialized world is older, more obese, and more likely to have epidural anesthesia, induced labor, and a larger baby than in generations past. That these factors may make dysfunctional labor more common is valuable information for the clinician, and should help guide decision-making, but should not necessarily result in more cesarean deliveries for dystocia. A labor disorder merely tells us something about the labor that should prompt extra scrutiny and reasoned analysis.
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Arguably, the most important virtue of the approach to labor we have encouraged is not in the numerical details of the curves, but in the way they can inform a logical and safe system of care during labor and delivery. We have advocated a method that allows a systematic measure of labor progress, provides an unequivocal language for communication about it, and encompasses a consistent and logical guide to decision-making.23 Furthermore, information derived from the curves has revealed clues to the risks inherent in certain aspects of labor and delivery.23,62,80,82-85 In aiming to restructure our fundamental understanding of normal labor progress, the guidelines raise a more general question about the incorporation of new research findings into practice. New observations are generally slow to enter professional guidelines and even slower to become common practice. This restraint allows new approaches to be confirmed by further study. Considering the conservative nature of that process, should we uncritically accept the recommended paradigm shift in labor management at this time, or should we await further confirmation of its value? We urge a cautious and considered approach. Adoption of uncorroborated new practices can have all sorts of unanticipated consequences, including harm to patients.
Conclusions The stated goal of the ACOG/SMFM Guidelines is to provide safe clinical strategies to prevent primary cesarean delivery. Whether the recommendations will achieve widespread acceptance remains to be seen. Our specialty has previously attempted to curtail the rising cesarean rate. Although success has been achieved in some individual institutions,94,95 the rising overall rate has not been significantly affected by the introduction of new guidelines. The recommendations of a national consensus conference on cesarean delivery in 198196 were, for example, largely ineffective. This is not surprising, given the difficulty of changing established practice in most areas of medicine.97-99
ajog.org Perhaps the pursuit of a desirable cesarean delivery rate will not bring us down the most worthy or productive path. The current cesarean rate is merely a symptom of a multifaceted and poorly understood process. Treating symptoms is rarely as satisfactory as is modifying or eliminating their source. If we direct our clinical and basic science investigations to the goal of practicing obstetrics in a manner that optimizes maternal and newborn outcomes, the ideal cesarean delivery rate, whatever it may be, will follow. The use of new databases, prospective designs, and new statistical methods to reassess data derived many years ago is quite reasonable. Novel findings deserve our respect and invite constructive scrutiny. Our overriding concern about the ACOG/SMFM recommendations is that they do not offer an encompassing paradigm for management. Friedman provided a nosology for dysfunctional labor, and, based on it, a system of care that is logical, reproducible, and easily applied. Failure to apply principles correctly can lead to specious diagnoses as well as untimely and inappropriate intervention.86 To adopt sweeping new guidelines for the assessment of labor that largely ignore antecedent obstetric practice is premature. One could infer from them that cultivation of the physical diagnostic skills necessary to become an astute obstetrician is no longer important. The guidelines never mention the need for measurement of fetal station, understanding the implications of the mechanism of labor, or any aspect of clinical cephalopelvimetry. They encourage considerably longer labors in first and second stage than generally practiced today, but they provide no evidence that such lengths would be safe for mother or baby. In fact, the guidelines regarding management of arrest disorders ignore the potential for any maternal or fetal risk. We do not know nearly enough about the association of long labor with chorioamnionitis, neonatal ischemic encephalopathy, birth injury, and maternal pelvic floor injury to abide the extended labors recommended by the guidelines.
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While the goals of the ACOG/SMFM Guidelines are admirable, their recommendations for the assessment of labor depart substantially from accepted norms, and no data yet exist to support the superiority or even the equivalence of the proposed paradigm for labor assessment and management to that which has served our patients well for many decades. Absent such data, It seems unwise to jettison 50 years of corroborated work with what Sir Robert Hutchison100 referred to as “too much zeal for the new and contempt for what is old.” Perhaps we should temper our enthusiasm and seek to verify what really constitutes best practice. The last thing anyone wants is for a new system to do a disservice to the women and babies entrusted to our care. REFERENCES 1. Millen KR, Kuo K, Zhao L, Gecsi K. Evidencebased guidelines in labor management. Obstet Gynecol Surv 2014;69:209-17. 2. Cahill AG, Tuuli MG. Labor in 2013: the new frontier. Am J Obstet Gynecol 2013;209:531-4. 3. El-Sayed YY. Diagnosis and management of arrest disorders: duration to wait. Semin Perinatol 2012;36:374-8. 4. Spong CY, Berghella V, Wenstrom KD, Mercer BM, Saade GR. Preventing the first cesarean delivery: summary of a joint Eunice Kennedy Shriver National Institute of Child Health and Human Development, Society for Maternal-Fetal Medicine, and American College of Obstetricians and Gynecologists Workshop. Obstet Gynecol 2012;120:1181-93. 5. American College of Obstetricians and Gynecologists; Society for Maternal-Fetal Medicine. Safe prevention of the primary cesarean delivery. Obstetric care consensus no. 1. Obstet Gynecol 2014;123:693-711. 6. Friedman EA. The graphic analysis of labor. Am J Obstet Gynecol 1954;68:1568-75. 7. Friedman EA. Primigravid labor: a graphicostatistical analysis. Obstet Gynecol 1955;6: 567-89. 8. Friedman EA. Labor in multiparas: a graphicostatistical analysis. Obstet Gynecol 1956;8: 691-703. 9. Friedman EA. Labor: clinical evaluation and management. New York: Appleton-CenturyCrofts; 1967. 10. Friedman EA. Labor: clinical evaluation and management, 2nd ed. New York: AppletonCentury-Crofts; 1978. 11. Zhang J, Troendle JF, Yancey MK. Reassessing the labor curve in nulliparous women. Am J Obstet Gynecol 2002;187:824-8. 12. Zhang J, Troendle J, Mikolajczyk R, Sundaram R, Beaver J, Fraser W. The natural
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