New data points to slower course of labor

Only recently has evidence emerged that challenges our long-held understanding of “normal” and “abnormal” labor. We now know there is a much wider range of normal labor progress in women who go on to have good labor outcomes. We have a new labor curve to guide us – one that shows us, for example, that active labor occurs most commonly after 6 cm dilation rather than 4 cm as we’d previously thought.

By appreciating this new labor paradigm, we can potentially have a significant impact on the cesarean rate in the United States. While our use of the older labor curve is not the only reason for the rise in cesarean deliveries over the last 30 years, it very likely has played a role. A study published in 2011 of more than 32,000 live births at a major academic hospital demonstrated that one of the most common reasons for primary cesarean is abnormal labor or arrest (Obstet Gynecol. 2011 Jul;118[1]:29-38).

Another study by the Consortium on Safe Labor – an analysis of labor and delivery information from more than 228,000 women across the United States – showed that half of the cesarean deliveries performed for dystocia in women undergoing labor induction were performed before 6 cm of cervical dilation and relatively soon after the previous cervical examination (Am J Obstet Gynecol. 2010 Oct; 203[4]: 326.e1–326.e10).

Our new labor paradigm brings to the forefront a host of new issues and questions about how we can best manage labor to optimize outcomes. In a way, recent discoveries about labor progress have highlighted a dearth of evidence and made “old” issues in labor management seem new and urgent.

As we strive to learn more, however, we are challenged to change our practices and behavior at the bedside with the evidence we currently have. By appreciating both the new labor curve and our current understanding of how labor induction, obesity, and other patient characteristics and clinical conditions can affect labor progress, we can expect that many women will simply progress much more slowly than was historically expected.

As long as we have indications of the well-being of the baby and the well-being of the mother, a slower but progressive labor in the first stage should not prompt us to intervene. We should no longer apply the standards of active-phase progress – standards that have traditionally driven our diagnoses of labor dystocia – until the patient has achieved 6 cm of dilation.

The labor curve that had shaped our thinking about normal and abnormal labor progress until recently was developed by Dr. Emanuel Friedman. Based on findings from a prospective cohort study of 500 nulliparous women, Dr. Friedman plotted labor progress with centimeters of cervical dilation on the Y-axis and time on the X-axis, and divided labor into several stages and phases. In this curve, the rate of change of cervical dilation over time started increasing significantly at 4 cm; this period of increasing slope defined the active phase of labor.

Abnormal labor progress in the active phase was then defined, based on the 95th percentile, as cervical dilation of less than 1.2 cm per hour for nulliparous women and less than 1.5 cm per hour for multiparous women. Based on Dr. Friedman’s work, a woman was deemed to be in active-phase arrest when she had no cervical changes for 2 hours or more while having adequate uterine contractions and cervical dilation of at least 4 cm. These concepts came to govern labor management.

The paradigm shifted when the Consortium on Safe Labor reported in 2010 on a retrospective cohort study of more than 62,000 women at 19 U.S. hospitals. The women had a singleton term gestation, spontaneous labor, vertex presentation, vaginal delivery, and a normal perinatal outcome. In their analysis of labor and delivery information, Dr. Jun Zhang of the National Institutes of Health’s Eunice Kennedy Shriver National Institute of Child Health and Human Development and his colleagues accounted for the fact that the exact times of cervical change are unknown.

They used modern statistical methods and analytical tools that took into account the specific nature of cervical dilation data – that cervical measurements are interval-censored (we never know the exact time when a woman’s cervix changes) and that multiple exams of the cervix in the same patient are not independent (Obstet Gynecol. 2010 Dec;116[6]:1281-7).

The methodology used in the Consortium study accounted for both the interval-censored and repeated-measures nature of cervical dilation data. It thus addressed analytical flaws in the previous approach to labor data, which was purely descriptive of the exam findings and did not consider the nature of the data itself.

Under the new analysis and in the larger, contemporary population of patients, the period of increasing slope was found to occur most commonly after 6 cm, not 4 cm. The slowest 5% of nulliparous women had cervical dilation of 0.4 cm per hour (with the median at 1.9 cm per hour), compared with 1.2 cm per hour (with a median of 3.0 cm per hour) as in the Friedman data.

Dr. Zhang’s study showed us that labor may take more than 6 hours to progress from 4 to 5 cm dilation, and more than 3 hours to progress from 5 to 6 cm dilation – a rate of progress that is significantly slower than what Dr. Friedman had described. The new data showed us, moreover, that from 4 cm-6 cm dilation, nulliparous and multiparous women progressed similarly slowly. Beyond 6 cm, multiparous women dilated more rapidly, with a steeper acceleration phase than previously described.

A consensus statement published in 2014 by the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) on “Safe Prevention of the Primary Cesarean Delivery” encourages use of the Consortium data to revisit the definition of labor dystocia. While the data “do not directly address an optimal duration for the diagnosis of active-phase protraction or labor arrest, [they] do suggest that neither should be diagnosed before 6 cm dilation” (Obstet Gynecol. 2014 Mar;123[3]:693-711).

The ACOG-SMFM statement makes a series of recommendations for managing the first and second stages of labor, based not only on the Consortium data but on a broader literature review. It recommends that if mother and fetus appear well, cesarean delivery for active-phase arrest in the first stage of labor be reserved for women of at least 6 cm of dilation with ruptured membranes who fail to progress despite 4 hours of adequate uterine activity, or at least 6 hours of oxytocin administration with inadequate uterine activity and no cervical change.

Regarding the latent phase of labor, the statement says that most women with a prolonged latent phase ultimately will enter the active phase with expectant management. It advises that a prolonged latent phase (for example, greater than 20 hours in nulliparous women and greater than 14 hours in multiparous women) should not be an isolated indication for cesarean delivery.

The consensus statement also recognizes recent data showing that women who undergo labor induction have an even slower “normal” course of labor, particularly a longer latent phase, than women who labor spontaneously. A retrospective cohort study of more than 5,000 women, for instance, found that before 6 cm, women whose labor is induced can spend up to 10 hours to achieve each 1 cm of dilation (Obstet Gynecol. 2012 Jun;119[6]:1113-8).

As long as maternal and fetal status are reassuring, the statement says, cesarean deliveries for failed induction of labor in the latent phase can be avoided by allowing longer durations of the latent phase (up to 24 hours) and by requiring that oxytocin be administered for 12-18 hours after membrane rupture before deeming induction a failure.

Each of these described recommendations were graded in the ACOG-SMFM consensus document as “strong” recommendations with “moderate quality evidence.”

Examining our standards

Moving forward, we must further develop and define our thresholds for identifying who will most benefit from a cesarean delivery. We have many specific aspects of labor management to address as well, such as the optimal timing of artificial membrane rupture and the safety and efficacy of different oxytocin protocols. We may also want to revisit recommendations for serial cervical assessment, possibly adjusting the intervals given our understanding of the new labor curve.

Under the new labor paradigm, moreover, we must think not only about the clinical decisions we make at the bedside, but about the decisions we make early in the labor management process.

The timing of admission is one such decision. A statement published in 2012 on “Preventing the First Cesarean Delivery” by ACOG, SMFM, and the Eunice Kennedy Shriver National Institute of Child Health and Human Development advises us to avoid admittance of women during the early latent phase of labor (Obstet Gynecol. 2012 Nov;120[5]:1181-93).

It may even be advisable that we consider admittance at higher cervical dilation. A study published this year shows that women admitted at less than 6 cm of dilation had an increased risk of cesarean delivery, compared with women admitted at higher cervical dilation (Am J Perinatol. 2016 Jan;33[2]:188-94). We have more to learn, but certainly, given what we know now about labor progress and the start of active labor, the timing of admission is an important factor to consider.

The second stage of labor, defined as the interval from complete cervical dilation through delivery of the fetus, presents many questions as well. There is a paucity of quality published data concerning what is normal, how long the stage should last, and how we should manage it. Historically, we have been taught to allow 2 hours of pushing for nulliparous women and 1 hour for multiparous women, when epidural anesthesia has not been administered, and to add an additional hour when epidural is used.

The 2014 ACOG-SMFM consensus statement recommends extending each of these limits by an hour, if maternal and fetal conditions permit, so that we allow at least 3 hours of pushing for nulliparous women and at least 2 hours for multiparous women before diagnosing arrest of labor in the second stage. Longer durations may be appropriate with the use of epidural anesthesia and on an individualized basis.

At this time, it is unclear whether there is any absolute maximum length of time beyond which all women in the second stage of labor should undergo cesarean delivery. We also still do not know the optimal technique for managing maternal pushing during the second stage. Should women with an epidural push right away or should they allow for a period of spontaneous descent? Many of the high-quality studies reported thus far that compare delayed and immediate pushing have limited applicability to current practice because they involved now-obsolete midpelvic forceps deliveries. A large multicenter randomized trial currently underway should provide us with some answers.

Dr. Cahill is an associate professor and chief of the division of maternal-fetal medicine in the department of obstetrics and gynecology at Washington University School of Medicine in St. Louis. She reported having no relevant financial disclosures.

Only recently has evidence emerged that challenges our long-held understanding of “normal” and “abnormal” labor. We now know there is a much wider range of normal labor progress in women who go on to have good labor outcomes. We have a new labor curve to guide us – one that shows us, for example, that active labor occurs most commonly after 6 cm dilation rather than 4 cm as we’d previously thought.

By appreciating this new labor paradigm, we can potentially have a significant impact on the cesarean rate in the United States. While our use of the older labor curve is not the only reason for the rise in cesarean deliveries over the last 30 years, it very likely has played a role. A study published in 2011 of more than 32,000 live births at a major academic hospital demonstrated that one of the most common reasons for primary cesarean is abnormal labor or arrest (Obstet Gynecol. 2011 Jul;118[1]:29-38).

Another study by the Consortium on Safe Labor – an analysis of labor and delivery information from more than 228,000 women across the United States – showed that half of the cesarean deliveries performed for dystocia in women undergoing labor induction were performed before 6 cm of cervical dilation and relatively soon after the previous cervical examination (Am J Obstet Gynecol. 2010 Oct; 203[4]: 326.e1–326.e10).

Our new labor paradigm brings to the forefront a host of new issues and questions about how we can best manage labor to optimize outcomes. In a way, recent discoveries about labor progress have highlighted a dearth of evidence and made “old” issues in labor management seem new and urgent.

As we strive to learn more, however, we are challenged to change our practices and behavior at the bedside with the evidence we currently have. By appreciating both the new labor curve and our current understanding of how labor induction, obesity, and other patient characteristics and clinical conditions can affect labor progress, we can expect that many women will simply progress much more slowly than was historically expected.

As long as we have indications of the well-being of the baby and the well-being of the mother, a slower but progressive labor in the first stage should not prompt us to intervene. We should no longer apply the standards of active-phase progress – standards that have traditionally driven our diagnoses of labor dystocia – until the patient has achieved 6 cm of dilation.

The labor curve that had shaped our thinking about normal and abnormal labor progress until recently was developed by Dr. Emanuel Friedman. Based on findings from a prospective cohort study of 500 nulliparous women, Dr. Friedman plotted labor progress with centimeters of cervical dilation on the Y-axis and time on the X-axis, and divided labor into several stages and phases. In this curve, the rate of change of cervical dilation over time started increasing significantly at 4 cm; this period of increasing slope defined the active phase of labor.

Abnormal labor progress in the active phase was then defined, based on the 95th percentile, as cervical dilation of less than 1.2 cm per hour for nulliparous women and less than 1.5 cm per hour for multiparous women. Based on Dr. Friedman’s work, a woman was deemed to be in active-phase arrest when she had no cervical changes for 2 hours or more while having adequate uterine contractions and cervical dilation of at least 4 cm. These concepts came to govern labor management.

The paradigm shifted when the Consortium on Safe Labor reported in 2010 on a retrospective cohort study of more than 62,000 women at 19 U.S. hospitals. The women had a singleton term gestation, spontaneous labor, vertex presentation, vaginal delivery, and a normal perinatal outcome. In their analysis of labor and delivery information, Dr. Jun Zhang of the National Institutes of Health’s Eunice Kennedy Shriver National Institute of Child Health and Human Development and his colleagues accounted for the fact that the exact times of cervical change are unknown.

They used modern statistical methods and analytical tools that took into account the specific nature of cervical dilation data – that cervical measurements are interval-censored (we never know the exact time when a woman’s cervix changes) and that multiple exams of the cervix in the same patient are not independent (Obstet Gynecol. 2010 Dec;116[6]:1281-7).

The methodology used in the Consortium study accounted for both the interval-censored and repeated-measures nature of cervical dilation data. It thus addressed analytical flaws in the previous approach to labor data, which was purely descriptive of the exam findings and did not consider the nature of the data itself.

Under the new analysis and in the larger, contemporary population of patients, the period of increasing slope was found to occur most commonly after 6 cm, not 4 cm. The slowest 5% of nulliparous women had cervical dilation of 0.4 cm per hour (with the median at 1.9 cm per hour), compared with 1.2 cm per hour (with a median of 3.0 cm per hour) as in the Friedman data.

Dr. Zhang’s study showed us that labor may take more than 6 hours to progress from 4 to 5 cm dilation, and more than 3 hours to progress from 5 to 6 cm dilation – a rate of progress that is significantly slower than what Dr. Friedman had described. The new data showed us, moreover, that from 4 cm-6 cm dilation, nulliparous and multiparous women progressed similarly slowly. Beyond 6 cm, multiparous women dilated more rapidly, with a steeper acceleration phase than previously described.

A consensus statement published in 2014 by the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) on “Safe Prevention of the Primary Cesarean Delivery” encourages use of the Consortium data to revisit the definition of labor dystocia. While the data “do not directly address an optimal duration for the diagnosis of active-phase protraction or labor arrest, [they] do suggest that neither should be diagnosed before 6 cm dilation” (Obstet Gynecol. 2014 Mar;123[3]:693-711).

The ACOG-SMFM statement makes a series of recommendations for managing the first and second stages of labor, based not only on the Consortium data but on a broader literature review. It recommends that if mother and fetus appear well, cesarean delivery for active-phase arrest in the first stage of labor be reserved for women of at least 6 cm of dilation with ruptured membranes who fail to progress despite 4 hours of adequate uterine activity, or at least 6 hours of oxytocin administration with inadequate uterine activity and no cervical change.

Regarding the latent phase of labor, the statement says that most women with a prolonged latent phase ultimately will enter the active phase with expectant management. It advises that a prolonged latent phase (for example, greater than 20 hours in nulliparous women and greater than 14 hours in multiparous women) should not be an isolated indication for cesarean delivery.

The consensus statement also recognizes recent data showing that women who undergo labor induction have an even slower “normal” course of labor, particularly a longer latent phase, than women who labor spontaneously. A retrospective cohort study of more than 5,000 women, for instance, found that before 6 cm, women whose labor is induced can spend up to 10 hours to achieve each 1 cm of dilation (Obstet Gynecol. 2012 Jun;119[6]:1113-8).

As long as maternal and fetal status are reassuring, the statement says, cesarean deliveries for failed induction of labor in the latent phase can be avoided by allowing longer durations of the latent phase (up to 24 hours) and by requiring that oxytocin be administered for 12-18 hours after membrane rupture before deeming induction a failure.

Each of these described recommendations were graded in the ACOG-SMFM consensus document as “strong” recommendations with “moderate quality evidence.”

Examining our standards

Moving forward, we must further develop and define our thresholds for identifying who will most benefit from a cesarean delivery. We have many specific aspects of labor management to address as well, such as the optimal timing of artificial membrane rupture and the safety and efficacy of different oxytocin protocols. We may also want to revisit recommendations for serial cervical assessment, possibly adjusting the intervals given our understanding of the new labor curve.

Under the new labor paradigm, moreover, we must think not only about the clinical decisions we make at the bedside, but about the decisions we make early in the labor management process.

The timing of admission is one such decision. A statement published in 2012 on “Preventing the First Cesarean Delivery” by ACOG, SMFM, and the Eunice Kennedy Shriver National Institute of Child Health and Human Development advises us to avoid admittance of women during the early latent phase of labor (Obstet Gynecol. 2012 Nov;120[5]:1181-93).

It may even be advisable that we consider admittance at higher cervical dilation. A study published this year shows that women admitted at less than 6 cm of dilation had an increased risk of cesarean delivery, compared with women admitted at higher cervical dilation (Am J Perinatol. 2016 Jan;33[2]:188-94). We have more to learn, but certainly, given what we know now about labor progress and the start of active labor, the timing of admission is an important factor to consider.

The second stage of labor, defined as the interval from complete cervical dilation through delivery of the fetus, presents many questions as well. There is a paucity of quality published data concerning what is normal, how long the stage should last, and how we should manage it. Historically, we have been taught to allow 2 hours of pushing for nulliparous women and 1 hour for multiparous women, when epidural anesthesia has not been administered, and to add an additional hour when epidural is used.

The 2014 ACOG-SMFM consensus statement recommends extending each of these limits by an hour, if maternal and fetal conditions permit, so that we allow at least 3 hours of pushing for nulliparous women and at least 2 hours for multiparous women before diagnosing arrest of labor in the second stage. Longer durations may be appropriate with the use of epidural anesthesia and on an individualized basis.

At this time, it is unclear whether there is any absolute maximum length of time beyond which all women in the second stage of labor should undergo cesarean delivery. We also still do not know the optimal technique for managing maternal pushing during the second stage. Should women with an epidural push right away or should they allow for a period of spontaneous descent? Many of the high-quality studies reported thus far that compare delayed and immediate pushing have limited applicability to current practice because they involved now-obsolete midpelvic forceps deliveries. A large multicenter randomized trial currently underway should provide us with some answers.

Dr. Cahill is an associate professor and chief of the division of maternal-fetal medicine in the department of obstetrics and gynecology at Washington University School of Medicine in St. Louis. She reported having no relevant financial disclosures.

Only recently has evidence emerged that challenges our long-held understanding of “normal” and “abnormal” labor. We now know there is a much wider range of normal labor progress in women who go on to have good labor outcomes. We have a new labor curve to guide us – one that shows us, for example, that active labor occurs most commonly after 6 cm dilation rather than 4 cm as we’d previously thought.

By appreciating this new labor paradigm, we can potentially have a significant impact on the cesarean rate in the United States. While our use of the older labor curve is not the only reason for the rise in cesarean deliveries over the last 30 years, it very likely has played a role. A study published in 2011 of more than 32,000 live births at a major academic hospital demonstrated that one of the most common reasons for primary cesarean is abnormal labor or arrest (Obstet Gynecol. 2011 Jul;118[1]:29-38).

Another study by the Consortium on Safe Labor – an analysis of labor and delivery information from more than 228,000 women across the United States – showed that half of the cesarean deliveries performed for dystocia in women undergoing labor induction were performed before 6 cm of cervical dilation and relatively soon after the previous cervical examination (Am J Obstet Gynecol. 2010 Oct; 203[4]: 326.e1–326.e10).

Our new labor paradigm brings to the forefront a host of new issues and questions about how we can best manage labor to optimize outcomes. In a way, recent discoveries about labor progress have highlighted a dearth of evidence and made “old” issues in labor management seem new and urgent.

As we strive to learn more, however, we are challenged to change our practices and behavior at the bedside with the evidence we currently have. By appreciating both the new labor curve and our current understanding of how labor induction, obesity, and other patient characteristics and clinical conditions can affect labor progress, we can expect that many women will simply progress much more slowly than was historically expected.

As long as we have indications of the well-being of the baby and the well-being of the mother, a slower but progressive labor in the first stage should not prompt us to intervene. We should no longer apply the standards of active-phase progress – standards that have traditionally driven our diagnoses of labor dystocia – until the patient has achieved 6 cm of dilation.

The labor curve that had shaped our thinking about normal and abnormal labor progress until recently was developed by Dr. Emanuel Friedman. Based on findings from a prospective cohort study of 500 nulliparous women, Dr. Friedman plotted labor progress with centimeters of cervical dilation on the Y-axis and time on the X-axis, and divided labor into several stages and phases. In this curve, the rate of change of cervical dilation over time started increasing significantly at 4 cm; this period of increasing slope defined the active phase of labor.

Abnormal labor progress in the active phase was then defined, based on the 95th percentile, as cervical dilation of less than 1.2 cm per hour for nulliparous women and less than 1.5 cm per hour for multiparous women. Based on Dr. Friedman’s work, a woman was deemed to be in active-phase arrest when she had no cervical changes for 2 hours or more while having adequate uterine contractions and cervical dilation of at least 4 cm. These concepts came to govern labor management.

The paradigm shifted when the Consortium on Safe Labor reported in 2010 on a retrospective cohort study of more than 62,000 women at 19 U.S. hospitals. The women had a singleton term gestation, spontaneous labor, vertex presentation, vaginal delivery, and a normal perinatal outcome. In their analysis of labor and delivery information, Dr. Jun Zhang of the National Institutes of Health’s Eunice Kennedy Shriver National Institute of Child Health and Human Development and his colleagues accounted for the fact that the exact times of cervical change are unknown.

They used modern statistical methods and analytical tools that took into account the specific nature of cervical dilation data – that cervical measurements are interval-censored (we never know the exact time when a woman’s cervix changes) and that multiple exams of the cervix in the same patient are not independent (Obstet Gynecol. 2010 Dec;116[6]:1281-7).

The methodology used in the Consortium study accounted for both the interval-censored and repeated-measures nature of cervical dilation data. It thus addressed analytical flaws in the previous approach to labor data, which was purely descriptive of the exam findings and did not consider the nature of the data itself.

Under the new analysis and in the larger, contemporary population of patients, the period of increasing slope was found to occur most commonly after 6 cm, not 4 cm. The slowest 5% of nulliparous women had cervical dilation of 0.4 cm per hour (with the median at 1.9 cm per hour), compared with 1.2 cm per hour (with a median of 3.0 cm per hour) as in the Friedman data.

Dr. Zhang’s study showed us that labor may take more than 6 hours to progress from 4 to 5 cm dilation, and more than 3 hours to progress from 5 to 6 cm dilation – a rate of progress that is significantly slower than what Dr. Friedman had described. The new data showed us, moreover, that from 4 cm-6 cm dilation, nulliparous and multiparous women progressed similarly slowly. Beyond 6 cm, multiparous women dilated more rapidly, with a steeper acceleration phase than previously described.

A consensus statement published in 2014 by the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) on “Safe Prevention of the Primary Cesarean Delivery” encourages use of the Consortium data to revisit the definition of labor dystocia. While the data “do not directly address an optimal duration for the diagnosis of active-phase protraction or labor arrest, [they] do suggest that neither should be diagnosed before 6 cm dilation” (Obstet Gynecol. 2014 Mar;123[3]:693-711).

The ACOG-SMFM statement makes a series of recommendations for managing the first and second stages of labor, based not only on the Consortium data but on a broader literature review. It recommends that if mother and fetus appear well, cesarean delivery for active-phase arrest in the first stage of labor be reserved for women of at least 6 cm of dilation with ruptured membranes who fail to progress despite 4 hours of adequate uterine activity, or at least 6 hours of oxytocin administration with inadequate uterine activity and no cervical change.

Regarding the latent phase of labor, the statement says that most women with a prolonged latent phase ultimately will enter the active phase with expectant management. It advises that a prolonged latent phase (for example, greater than 20 hours in nulliparous women and greater than 14 hours in multiparous women) should not be an isolated indication for cesarean delivery.

The consensus statement also recognizes recent data showing that women who undergo labor induction have an even slower “normal” course of labor, particularly a longer latent phase, than women who labor spontaneously. A retrospective cohort study of more than 5,000 women, for instance, found that before 6 cm, women whose labor is induced can spend up to 10 hours to achieve each 1 cm of dilation (Obstet Gynecol. 2012 Jun;119[6]:1113-8).

As long as maternal and fetal status are reassuring, the statement says, cesarean deliveries for failed induction of labor in the latent phase can be avoided by allowing longer durations of the latent phase (up to 24 hours) and by requiring that oxytocin be administered for 12-18 hours after membrane rupture before deeming induction a failure.

Each of these described recommendations were graded in the ACOG-SMFM consensus document as “strong” recommendations with “moderate quality evidence.”

Examining our standards

Moving forward, we must further develop and define our thresholds for identifying who will most benefit from a cesarean delivery. We have many specific aspects of labor management to address as well, such as the optimal timing of artificial membrane rupture and the safety and efficacy of different oxytocin protocols. We may also want to revisit recommendations for serial cervical assessment, possibly adjusting the intervals given our understanding of the new labor curve.

Under the new labor paradigm, moreover, we must think not only about the clinical decisions we make at the bedside, but about the decisions we make early in the labor management process.

The timing of admission is one such decision. A statement published in 2012 on “Preventing the First Cesarean Delivery” by ACOG, SMFM, and the Eunice Kennedy Shriver National Institute of Child Health and Human Development advises us to avoid admittance of women during the early latent phase of labor (Obstet Gynecol. 2012 Nov;120[5]:1181-93).

It may even be advisable that we consider admittance at higher cervical dilation. A study published this year shows that women admitted at less than 6 cm of dilation had an increased risk of cesarean delivery, compared with women admitted at higher cervical dilation (Am J Perinatol. 2016 Jan;33[2]:188-94). We have more to learn, but certainly, given what we know now about labor progress and the start of active labor, the timing of admission is an important factor to consider.

The second stage of labor, defined as the interval from complete cervical dilation through delivery of the fetus, presents many questions as well. There is a paucity of quality published data concerning what is normal, how long the stage should last, and how we should manage it. Historically, we have been taught to allow 2 hours of pushing for nulliparous women and 1 hour for multiparous women, when epidural anesthesia has not been administered, and to add an additional hour when epidural is used.

The 2014 ACOG-SMFM consensus statement recommends extending each of these limits by an hour, if maternal and fetal conditions permit, so that we allow at least 3 hours of pushing for nulliparous women and at least 2 hours for multiparous women before diagnosing arrest of labor in the second stage. Longer durations may be appropriate with the use of epidural anesthesia and on an individualized basis.

At this time, it is unclear whether there is any absolute maximum length of time beyond which all women in the second stage of labor should undergo cesarean delivery. We also still do not know the optimal technique for managing maternal pushing during the second stage. Should women with an epidural push right away or should they allow for a period of spontaneous descent? Many of the high-quality studies reported thus far that compare delayed and immediate pushing have limited applicability to current practice because they involved now-obsolete midpelvic forceps deliveries. A large multicenter randomized trial currently underway should provide us with some answers.

Dr. Cahill is an associate professor and chief of the division of maternal-fetal medicine in the department of obstetrics and gynecology at Washington University School of Medicine in St. Louis. She reported having no relevant financial disclosures.