The second stage of labor.

The second stage of labor extends from complete cervical dilatation to delivery. During this stage, descent and rotation of the presenting part occur as the fetus passively negotiates its passage through the birth canal. Generally, descent begins during the deceleration phase of dilatation as the cervix is drawn upward around the fetal presenting part. The most common means of assessing the normality of the second stage of labor is to measure its duration, but progress can be more meaningfully gauged by measuring the change in fetal station as a function of time. Accurate clinical identification and evaluation of differences in patterns of fetal descent are necessary to assess second stage of labor progress and to make reasoned judgments about the need for intervention. Three distinct graphic abnormalities of the second stage of labor can be identified: protracted descent, arrest of descent, and failure of descent. All abnormalities have a strong association with cephalopelvic disproportion but may also occur in the presence of maternal obesity, uterine infection, excessive sedation, and fetal malpositions. Interpretation of the progress of fetal descent must be made in the context of other clinically discernable events and observations. These include fetal size, position, attitude, and degree of cranial molding and related evaluations of pelvic architecture and capacity to accommodate the fetus, uterine contractility, and fetal well-being. Oxytocin infusion can often resolve an arrest or failure of descent or a protracted descent caused by an inhibitory factor, such as a dense neuraxial block. It should be used only if thorough assessment of fetopelvic relationships reveals a low probability of cephalopelvic disproportion. The value of forced Valsalva pushing, fundal pressure, and routine episiotomy has been questioned. They should be used selectively and where indicated.

The active phase of labor.

The active phase of labor begins at various degrees of dilatation when the rate of dilatation transitions from the relatively flat slope of the latent phase to a more rapid slope. No diagnostic manifestations demarcate its onset, other than accelerating dilatation. It ends with apparent slowing of dilatation, a deceleration phase, which is usually short in duration and frequently undetected. Several aberrant labor patterns can be detected during the active phase, including protracted dilatation, arrest of dilatation, prolonged deceleration phase and failure of descent. Underlying factors may include cephalopelvic disproportion, excessive neuraxial block, poor uterine contractility, fetal malpositions, malpresentations, uterine infection, maternal obesity, advanced maternal age and previous cesarean delivery. When an active-phase disorder is identified, cesarean delivery is justifiable if there is compelling clinical evidence of disproportion. A prolonged deceleration disorder is strongly associated with disproportion and second stage abnormalities. Shoulder dystocia may occur if vaginal delivery eventuates. This review discusses several issues raised by the introduction of new clinical practice guidelines for labor management.

Dysfunctional labor and delivery: adverse effects on offspring.

There is no doubt that parturition can produce fetal and neonatal adversity, but the frequency with which this occurs is uncertain, particularly in modern healthcare settings. Moreover, there is a paucity of recent studies in this area. Substantial challenges impede epidemiologic study of the effect of parturition on offspring. Randomized trials would be ethically fraught. Therefore, large observational samples with detailed data concerning labor and delivery events are needed. Importantly, long-term follow-up of infants is necessary to reach reliable conclusions. Few such data sets exist, and it is difficult, expensive, and time-consuming to create and to study them. Reports of immediate newborn condition in relation to the antecedent labor are helpful, but this evidence is an imperfect predictor of long-term neurologic status. In this review, we endeavor to summarize existing information about the relationship between objectively defined abnormalities of labor progress and long-term disability in offspring. The only data available are from collected experiential information on outcomes stratified according to labor and delivery events. Most studies do not ensure against confounding by the many concurrent conditions that may affect outcome, or use inconsistent criteria to define abnormal labor. According to the best available evidence, dysfunctional labor patterns are potentially associated with poor outcomes for surviving infants. The question of whether these adverse effects can be mitigated by early diagnosis and expeditious management deserves to be answered, but cannot be at this time. In the absence of more conclusive results from well-designed studies, we can conclude that the best interests of offspring are served by adhering to evidence-based paradigms for the prompt identification and treatment of dysfunctional labor patterns.

The latent phase of labor.

The latent phase of labor extends from the initiation of labor to the onset of the active phase. Because neither margin is always precisely identifiable, the duration of the latent phase often can only be estimated. During this phase, the cervix undergoes a process of rapid remodeling, which may have begun gradually weeks before. As a consequence of extensive changes in its collagen and ground substance, the cervix softens, becomes thinner and dramatically more compliant, and may dilate modestly. All of these changes prepare the cervix for the more rapid dilatation that will occur during the active phase to follow. For the clinician, it is important to recognize that the latent phase may normally extend for many hours. The normal limit for the duration of the latent phase should be considered to be approximately 20 hours in a nullipara and 14 hours in a multipara. Factors that have been associated with a prolonged latent phase include deficient prelabor or intrapartum cervical remodeling, excessive maternal analgesia or anesthesia, maternal obesity, and chorioamnionitis. Approximately 10% of women with a prolonged latent phase are actually in false labor, and their contractions eventually abate spontaneously. The management of a prolonged latent phase involves either augmenting uterine activity with oxytocin or providing a sedative-induced period of maternal rest. Both are equally effective in advancing the labor to active phase dilatation. A very long latent phase may be a harbinger of other labor dysfunctions.

Clinical evaluation of labor: an evidence- and experience-based approach.

During labor mother and fetus are evaluated at intervals to assess their well-being and determine how the labor is progressing. These assessments require skillful physical diagnosis and the ability to translate the acquired information into meaningful prognostic decision-making. We describe a coordinated approach to the assessment of labor. Graphing of serial measurements of cervical dilatation and fetal station creates "labor curves," which provide diagnostic and prognostic information. Based on these curves we recognize nine discrete labor abnormalities. Many may be related to insufficient or disordered contractile mechanisms. Several factors are strongly associated with development of labor disorders, including cephalopelvic disproportion, excess analgesia, fetal malpositions, intrauterine infection, and maternal obesity. Clinical cephalopelvimetry involves assessing pelvic traits and predicting their effects on labor. These observations must be integrated with information derived from the labor curves. Exogenous oxytocin is widely used. It has a high therapeutic index, but is easily misused. Oxytocin treatment should be restricted to situations in which its potential benefits clearly outweigh its risks. This requires there be a documented labor dysfunction or a legitimate medical reason to shorten the labor. Normal labor and delivery pose little risk to a healthy fetus; but dysfunctional labors, especially if stimulated excessively by oxytocin or terminated by complex operative vaginal delivery, have the potential for considerable harm. Conscientiously implemented, the approach to the evaluation of labor outlined in this review will result in a reasonable cesarean rate and minimize risks that may accrue from the labor and delivery process.

Guidelines for labor assessment: failure to progress?

The ongoing debate about what models of cervical dilatation and fetal descent should guide clinical decision-making has sown uncertainty among obstetric practitioners. We previously argued that the adoption of recently published labor assessment guidelines promoted by the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine may have been premature. Before accepting any new clinical approaches as the standard of care, their underlying hypotheses should be thoroughly tested to ensure they are at least equivalent (or, preferably, superior) to existing management paradigms. Some of the apparent urgency to subscribe to new clinical tactics has been fueled by legitimate concerns about the rise in the cesarean delivery rate over the past several decades. A major contributor to this change in practice patterns is that more cesarean deliveries are being done for diagnoses that fall under the rubric of dystocia than ever before. As a consequence, traditional labor curves-fundamental for assessing labor progress-and the practice paradigms associated with them have received intense scrutiny as a possible contributor to this delivery trend. Moreover, the recent proposal of new labor curves and accompanying management guidelines has, understandably, fed the appetite to correct a perceived problem. However, the cesarean delivery rate rose most rapidly during decades when there was no major change in traditional labor curves or in the guidelines for their interpretation. Also, during the years since the new guidelines were first published, there has been no major fall in cesarean delivery frequency. This raises the question of whether there was truly a fundamental flaw in the traditional labor management paradigms or whether their proper interpretation and use had been somehow forgotten, ignored, or corrupted. More important, existing studies have shown that application of the new guidelines often (but not always) results in a modest fall in the cesarean delivery rate, but that this change may be accompanied by significant increases in maternal and neonatal morbidity. These results strongly suggest more caution in the adoption of the American College of Obstetricians and Gynecologists / Society for Maternal-Fetal Medicine labor assessment recommendations. They are based on a hypothesis that has yet to undergo thorough evaluation of its risks and benefits.

The assessment of labor: a brief history.

In the 1930s, investigators in the US, Germany and Switzerland made the first attempts to quantify the course of labor in a clinically meaningful way. They emphasized the rupture of membranes as a pivotal event governing labor progress. Attention was also placed on the total number of contractions as a guide to normality. Beginning in the 1950s, Friedman determined that changes in cervical dilatation and fetal station over time were the most useful parameters for the assessment of labor progress. He showed all normal labors had similar patterns of dilatation and descent, differing only in the durations and slopes of their component parts. These observations led to the formulation of criteria that elevated the assessment of labor from a rather arbitrary exercise to one guided by scientific objectivity. Researchers worldwide confirmed the basic nature of labor curves and validated their functionality. This system allows us to quantify the effects of parity, analgesia, maternal obesity, prior cesarean, maternal age, and fetal presentation and position on labor. It permits analysis of outcomes associated with labor aberrations, quantifies the effectiveness of treatments and assesses the need for cesarean delivery. Also, dysfunctional labor patterns serve as indicators of short- and long-term risks to offspring. We still lack the necessary translational research to link the physiologic manifestations of uterine contractility with changes in dilatation and descent. Recent efforts to interpret electrohysterographic patterns hold promise in this regard, as does preliminary exploration into the molecular basis of dysfunctional labor. For now, the clinician is best served by a system of labor assessment proposed more than 60 years ago and embellished upon in considerable detail since.

Perils of the new labor management guidelines.

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.

Misguided guidelines for managing labor.

In a recent review we expressed concerns about new guidelines for the assessment and management of labor recommended jointly by the American Congress of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM). These guidelines are based heavily on a new concept of how cervical dilatation and fetal descent progress, derived from the work of Zhang et al. In their Viewpoint article they have addressed, but not allayed, the concerns we described in our review. We assert that the dilatation curve promulgated by Zhang et al cannot be reconciled with direct clinical observation. Even if they were correct, however, it still does not follow that the ACOG/SMFM guidelines should recommend replacing the coherent system of identifying and managing labor aberrations described by Friedman. That system is grounded in well-established clinical principles based on decades of use and the objectively documented association of some labor abnormalities with poor fetal and maternal outcomes. Recommendations for new clinical management protocols should require the demonstration of superior outcomes through extensive, preferably prospective, assessment. Using untested guidelines for the management of labor may adversely affect women and children. Even if those guidelines were to reduce the currently excessive cesarean delivery rate, the price of that benefit is likely to be a trade-off in harm to parturients and their offspring. The nature and degree of that harm needs to be documented before considering adoption of the guidelines.

Obstetric practice guidelines: labor's love lost?

Implementation of clinical practice guidelines may moderate health care costs, improve care, reduce medicolegal liability, and provide a uniformity in care allowing meaningful investigation of treatments and outcomes. However, new guidelines are often uncritically embraced by clinicians, risk management organizations, insurance companies, and the courts as the standard of care. Adoption of incompletely vetted recommendations can lead to patient harm. Recent recommendations made by the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine for assessment and management of labor provide an example of well-intended guidelines adopted uncritically. Ideally, but unattainably, each step in a practice guideline would be supported by results of prospective randomized trials. Usually, data from lower on the hierarchy of proof are included, and the personal or institutional preferences of the guideline developers influence the final product. These multiple resources help illuminate critical issues and balance competing perspectives, but can introduce biases that become embedded in our practice. The new labor management guidelines, which were never shown to be superior (or even equivalent) to current standards, have achieved widespread acceptance. Although they provide a formula for reducing the cesarean rate, they do so without concern for their potentially adverse effects on maternal or neonatal outcome. New guidelines should be outcome-based and address how to practice obstetrics to yield the best possible results for mother and baby.