Clinical Opinion
www.AJOG .org
OBSTETRICS
Labor in 2013: the new frontier
Alison G. Cahill, MD, MSCI; Methodius G. Tuuli, MD, MPH
I
ncredibly, labor is the new frontier in
2013 and arguably our most important one in obstetrics. Although women
labor and deliver more than 3 million
times per year in the United States,1 what
we considered normal and abnormal
labor was incorrect for decades. It is only
in the last 10 years that the correct shape
of the first stage of normal labor has been
described. And with these discoveries
have come additional challenges. We are
at once faced with both the realization
that much more work is left to be done
to provide good scientific evidence for
management of labor to optimize outcomes as well as the clinical challenge to
change behavior at the bedside with the
important evidence that we have recently
been given.
The objective of this review is to highlight critical aspects of both new data and
knowledge gaps for clinicians at the forefront of practice change as well as scientists working to generate the evidence
needed to guide clinical practice.
Friedman’s labor curve
In 1955, Emanuel Friedman2 described
the labor of 500 nulliparous women in a
convenience sample, plotting their labor
progress in centimeters of cervical dilation on the Y-axis and time on the X-axis,
generating a sigmoid-shaped curve. This
curve, despite its descriptive and nonrepresentative nature, came to define
From the Department of Obstetrics and
Gynecology, Washington University,
St. Louis, MO.
Received Feb. 2, 2013; revised March 18, 2013;
accepted April 3, 2013.
The authors report no conflict of interest.
Reprints: Alison G. Cahill, MD, MSCI,
Department of Obstetrics and Gynecology,
Division of Maternal-Fetal Medicine, Washington
University School of Medicine, St. Louis,
MO 63110. [email protected].
0002-9378/$36.00
ª 2013 Mosby, Inc. All rights reserved.
http://dx.doi.org/10.1016/j.ajog.2013.04.016
Despite the frequency with which obstetrics providers manage labor, evidence has
emerged in the past few years challenging our historical understanding of normal labor
progress over time. We are also confronted with the dearth of evidence to guide the
optimal management of labor. With these data, we are presented with both the challenge
of changing practice at the bedside and the opportunity for new discovery to optimize
labor and delivery outcomes. Given the sheer frequency of labor and delivery, changes
that improve outcomes even by a small magnitude have the potential to dramatically
impact labor-associated morbidity at the population level.
Key words: first stage, labor, second stage
normal and abnormal labor over the
following 40 years.
In 2002, Zhang et al3 discovered that
the common understanding of normative labor progress in the first stage was
likely incorrect and further validated
the corrected first-stage labor curve in a
large multicenter cohort. Specifically,
Zhang et al3 discovered an analytic flaw
in the historical approach to labor data;
it was assumed that the time of cervical
change was known. In fact, the exact
time when cervical dilation changes
from one measure to another is unknown, and thus, cervical dilation data
are interval censored.
What is known is the time at which a
patient has an examination and that her
cervix changed sometime between the
last and the current cervical dilation.
Furthermore, cervical examinations during labor are repeated measures that are
correlated, violating the assumption of
independence needed for many statistical
methods. Thus, appropriate analytic
tools for labor progress must take into
account both the interval-censored and
repeated-measures nature of cervical
dilation data. Such analyses have reshaped our understanding of the normal first
stage. Specifically, it appears that active
labor, or the period of increasing slope,
occurs most commonly after 6 cm dilation, not 4 cm. Furthermore, the deceleration phase once described at the end of
the first stage was most likely an analytic
artifact of the prior analytic approach.
Unintended consequences
When obstetric providers perceive abnormalities in labor progress in the first
stage of labor, we intervene, with the
intent to optimize outcomes. Although
measures such as artificial rupture of
membranes with intrauterine pressure
catheter placement and oxytocin augmentations are used in an attempt to
correct abnormal progress in the first
stage, cesarean delivery is commonly
used. The 100% increase in the cesarean
rate in the last 30 years (from 16.5%
in 1980 to 32.8% in 2010)1 has been
multifactorial, meaning the entire rise
cannot be blamed solely on the use of
the flawed Friedman curves. However,
recent data have demonstrated that one
of the most common reasons for first
cesarean is abnormal labor or arrest.4
Zhang et al5 in 2010 described the
pattern of modern cesarean delivery, and
specifically as it relates to labor progress,
among 228,668 women. They observed
that a large proportion of women undergoing cesarean for diagnoses of failed
labor progress did so at disappointingly
early dilations and after a relatively short
time interval after their previous cervical
examination. For example, among nulliparous women undergoing cesarean for
labor failure, 38% of those in spontaneous
labor and 63% of those being induced
had their cesarean performed at or before
6 cm dilation was reached.
If the observations in cesarean for arrest
diagnoses since the modern correction
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Clinical Opinion
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in shape of the labor curve are correct,
then we find ourselves faced with perhaps
an even greater challenge than the scientific discoveries that question accepted
truths: changing our behavior. Some have
been resistant to implementing Zhang’s
curve3 because of concerns that this
modern curve is the result of modern
obstetrical practices such as the high rate
of cesarean, change in rates of obesity, and
increased epidural use.3 Although this
criticism is thoughtful, we believe it is
unfounded. The increased use of interventions that may affect labor progress
argue for (rather than against) the need
for newer standards to reflect contemporary practice. Furthermore, the same basic
patterns of labor progress were replicated
when Zhang et al3 applied the same
methodology to data from the 1960s. This
suggests that the differences stem more
from differences in the methodology used
in older studies than from differences in
patients.3
Reconsidering current clinical
standards
We find in major texts in obstetrics, such
as Williams Obstetrics, the suggestion of
a clinical standard to examine women
every 2-3 hours while in labor,6 and
references to prior work that standard
protocols for the management of labor
resulted in improved outcomes.4 One
practical consideration we are challenged with now is whether the recommendations for the intervals of serial
cervical assessment should be revisited.
For example, might we consider longer
intervals between cervical assessments,
such as prior to 6 cm, when we now
estimate that demonstrable change, even
in women who will ultimately deliver a
normal infant vaginally, might take
many hours?7 Similarly, if the majority of
women will reach complete dilation,
regardless of parity, within 30 minutes of
having an examination of 9 cm, should
the recommended intervals of cervical
examination be shorter in the later part
of the active phase of labor?
Attempts have been made in the recent past to alter earlier guidelines for
diagnosing arrest of labor. Based on a
prospective protocol evaluation, Rouse
et al8 reported that extending the
minimum period of oxytocin augmentation for active-phase labor arrest from
2 to at least 4 hours was effective and
safe. Most recently Spong et al9 published a summary of expert opinions
from the consensus conference on Preventing the First Cesarean, highlighting
the consequences of a disconnect between old labor management despite
modern curves as well as recommendations for possible new standards for
definitions of abnormal labor and arrest.
We might also consider the opportunity to make changes in the practice of
labor management further upstream.
That is, perhaps our generation of data
that is no longer likely to be clinically
useful other than leading to temptation
of an iatrogenic arrest disorder diagnosis,
such as cervical examinations every 2
hours prior to 6 cm dilation, is no longer
a reasonable practice pattern based on
our current evidence. Furthermore, we
might consider that some of the best data
regarding active labor management10,11
used definitions of labor and labor
progress that do not precisely reflect our
current understanding of the labor curve.
Thus, additional research regarding optimal labor management strategies in the
new labor paradigm is likely warranted.
Other unresolved aspects of labor
management in the first stage such as
the optimal timing of artificial rupture
of membranes, efficacy, and safety of
different oxytocin protocols also deserve
further study.
Does one size fit all?
Several recent publications have described inherent differences in the progress of the first stage of labor based on
specific patient characteristics or clinical
conditions. For example, our published
data12 demonstrate that labor progress to
complete cervical dilation is slower in
women undergoing induction compared
with those laboring spontaneously. Other
factors, such as maternal obesity,13 gestational age during labor, and even fetal
sex14 have been shown to have an impact
on median labor progress. Thus, the
progress made by Zhang et al7 in describing the overall expected median
progress for a population is only the
beginning. The observed shifts in labor
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curves associated with individual factors
must be further investigated and translated into an integrated and clinically
useful tool that can be used by clinicians
at the individual patient’s bedside.
The second stage
If the first stage of labor represents an
opportunity to improve practice and
outcomes, the second stage is at least
as important. Expectations of normal
duration of the second stage have been
guided for many years by findings of the
Friedman study2 with minor modifications based on later studies,15 although
forceps were liberally used (>50% in the
Friedman study) to truncate the second
stage. The recent document by Spong
et al9 recommends extending prior
proposed limits for diagnoses of arrest in
the second stage by an hour. However,
the impact of these recommendations on
maternal and neonatal outcomes deserves investigation.
There is a paucity of quality published
data to guide clinical management of
the second stage of labor in modern
practice to achieve optimal outcomes.
For example, 2 questions encountered in
every day practice that remain are: when
should pushing start and how should
women push? The largest randomized
trial to date addressing second-stage
management with passive descent vs
immediate pushing at complete dilation,
of 1862 nulliparous women, was reported
in 2000. This study showed a reduction in
composite birth morbidity associated
with delayed pushing.16 Similarly, a metaanalysis reported in 2008 suggested
that, compared with immediate pushing,
delayed pushing was associated with
increased spontaneous vaginal deliveries,
decreased operative vaginal deliveries,
and decreased duration of active pushing.17 Given these findings, the Association of Women’s Health, Obstetric and
Neonatal Nurses published guidelines in
2008 recommending delayed pushing in
the second stage of labor unless contraindicated by maternal or fetal condition.
Unfortunately, the studies cited in
previous text have limited applicability to
current obstetrical practice. For example,
the significant findings in the largest trial
were driven largely by a reduction in
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midpelvic forceps deliveries, which are
virtually obsolete in modern obstetric
practice in the United States.18 The study
also reported a significantly higher rate of
abnormal cord pH when delayed pushing
was used (4.5% compared with 1.8%,
relative risk, 2.45; 95% confidence interval, 1.35e4.43), although the authors
used an unconventional definition of
abnormal cord pH (venous pH <7.15 or
arterial pH <7.10.) and noted that the
increase in abnormal cord pH did not
translate into a demonstrable increase in
neonatal morbidity and mortality.
The methodology of many of the other
trials has also been challenged. An updated meta-analysis suggests no significant
benefit of delayed pushing when only
studies judged to be of high methodological quality are pooled.19 Furthermore,
what is consistent across studies is that
delayed pushing lengthens the second
stage. Three recent publications suggest
that as the second stage of labor continues, beyond the first hour, regardless of
management approach, there is an associated dose-response increase in maternal
and neonatal morbidities.20-22 Accordingly, the competing risks of longer second stage and a clinical management
strategy that may not result in improved
outcomes deserve further study.
Evidence on how women should push
in the second stage is equally sparse.
A recent meta-analysis of randomized
trials comparing spontaneous pushing
with Valsalva pushing in the second
stage of labor included only 3 small
studies characterized by the authors as
“sparse, diverse, and some flawed.”23 The
pooled analysis suggested that duration
of the second stage was longer with
spontaneous pushing, but no statistical
differences were noted in operative deliveries (3 studies; 425 women; pooled
relative risk, 0.70; 95% confidence interval, 0.34e1.43), perineal lacerations,
postpartum hemorrhage, and neonatal
outcomes. Although Valsalva pushing
appeared to have a negative effect on
urodynamic measures at 3 months, this
was based on results of only 1 small
study.24 Thus, studies on how best to
manage the second stage of labor might
offer as much, if not greater opportunity
for research as the first stage. Such
studies should include effects of the
various management strategies, not just
on efficacy and short-term outcomes but
also on long-term consequences such as
maternal pelvic floor morbidity.
Opportunity for practice change and
research
In the coming years, we have the opportunity to use currently available data to
make changes to practice that might
optimize efficacy and safety of the most
common clinical entity seen in obstetrics:
labor. Small changes that improve outcomes have the potential to dramatically
impact labor-associated morbidity at the
population level, given the sheer frequency of its occurrence. For example,
the recent summary document from
Spong et al9 highlights the potentially
significant impact misdiagnoses of labor
arrest disorders can have on the primary cesarean rate and the opportunity
changes in practice might offer our
patients. However, much scientific work
remains regarding optimal management
of both the first and the second stage of
labor to improve efficacy and safety.
These studies should focus on rigorous methodology rather than preconceived notions of the anticipated results.
Although observational data can provide
some insight, there is also high risk for
selection bias and confounding in laborrelated studies, such that randomized
controlled trials should be used whenever possible to produce the best-quality
evidence to guide clinical practice. We
look forward to this new frontier with
anticipation and hope.
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Clinical Opinion
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