The New England Journal of Medicine
Original Article
Volume 345:3-8

July 5, 2001

Number 1



Risk of Uterine Rupture during Labor among Women with a Prior Cesarean
Delivery
Mona Lydon-Rochelle, Ph.D., Victoria L. Holt, Ph.D., Thomas R. Easterling,
M.D., and Diane P. Martin, Ph.D.
ABSTRACT
Background Each year in the United States, approximately 60 percent of women
with a prior cesarean delivery who become pregnant again attempt labor.
Concern persists that a trial of labor may increase the risk of uterine
rupture, an uncommon but serious obstetrical complication.
Methods We conducted a population-based, retrospective cohort analysis using
data from all primiparous women who gave birth to live singleton infants by
cesarean section in civilian hospitals in Washington State from 1987 through
1996 and who delivered a second singleton child during the same period (a
total of 20,095 women). We assessed the risk of uterine rupture for
deliveries with spontaneous onset of labor, those with labor induced by
prostaglandins, and those in which labor was induced by other means; these
three groups of deliveries were compared with repeated cesarean delivery
without labor.
Results Uterine rupture occurred at a rate of 1.6 per 1000 among women with
repeated cesarean delivery without labor (11 women), 5.2 per 1000 among
women with spontaneous onset of labor (56 women), 7.7 per 1000 among women
whose labor was induced without prostaglandins (15 women), and 24.5 per 1000
among women with prostaglandin-induced labor (9 women). As compared with the
risk in women with repeated cesarean delivery without labor, uterine rupture
was more likely among women with spontaneous onset of labor (relative risk,
3.3; 95 percent confidence interval, 1.8 to 6.0), induction of labor without
prostaglandins (relative risk, 4.9; 95 percent confidence interval, 2.4 to
9.7), and induction with prostaglandins (relative risk, 15.6; 95 percent
confidence interval, 8.1 to 30.0).
Conclusions For women with one prior cesarean delivery, the risk of uterine
rupture is higher among those whose labor is induced than among those with
repeated cesarean delivery without labor. Labor induced with a prostaglandin
confers the highest risk.
  _____

Each year in the United States, approximately 60 percent of women with a
prior cesarean delivery have a trial of labor in a subsequent pregnancy.
Concern persists that a trial of labor may increase the risk of maternal
complications as compared with elective cesarean delivery. Such
complications include uterine rupture, which is uncommon but serious and may
result in hysterectomy, urologic injury, a need for blood transfusion,
maternal death, and perinatal complications, including neurologic impairment
and death. 1 <http://content.nejm.org/cgi/content/full/345/1/#R1> , 2
<http://content.nejm.org/cgi/content/full/345/1/#R2> , 3
<http://content.nejm.org/cgi/content/full/345/1/#R3> , 4
<http://content.nejm.org/cgi/content/full/345/1/#R4>
Population-based studies of the relation between a trial of labor and
uterine rupture have had methodologic limitations and have produced
inconsistent findings. A study in Nova Scotia, Canada, reported that a trial
of labor was not significantly associated with uterine rupture; however, in
that study, too few women had uterine rupture to provide meaningful results.
2 <http://content.nejm.org/cgi/content/full/345/1/#R2>  In contrast, studies
in Switzerland and California demonstrated a significantly higher risk of
uterine rupture among women undergoing a trial of labor than among women
with elective repeated cesarean delivery. 1
<http://content.nejm.org/cgi/content/full/345/1/#R1> , 5
<http://content.nejm.org/cgi/content/full/345/1/#R5>  However, these studies
did not control for parity or the number of prior cesarean deliveries. In
addition, although the rates of induction of labor among women with prior
cesarean delivery have been increasing, none of these studies distinguished
the risk of uterine rupture associated with a trial of labor with induction
of labor from that without induction. 6
<http://content.nejm.org/cgi/content/full/345/1/#R6>  We used statewide
linked birth-certificate and hospital-discharge data to examine the risk of
uterine rupture associated with spontaneous onset of labor, induction of
labor not involving prostaglandins, induction of labor with prostaglandins,
and repeated cesarean delivery without labor among women with one prior
cesarean delivery.
Methods
Study Design
We conducted a population-based, retrospective cohort analysis using data
obtained from the Washington State Birth Events Record Database. This data
base links more than 95 percent of birth certificates in Washington State
with maternal and infant records from the Comprehensive Hospital Discharge
Reporting System for the hospitalization associated with delivery. The
present cohort included all primiparous women who gave birth to live
singleton infants by cesarean section in civilian hospitals in Washington
from January 1, 1987, through December 31, 1996, and who delivered a second
singleton child in Washington during the same period (a total of 20,525
women). Because a variable indicating that the women had a second cesarean
section without labor ("repeat cesarean no labor") was not added to the
birth certificates until 1989, we excluded the 430 women who had a second
delivery before 1989. After the exclusion, 20,095 subjects remained for
analysis. Demographic variables were derived from first and second birth
certificates, information on payers from maternal and infant
hospitalization-discharge data for the second delivery, and medical
information from maternal and infant hospitalization-discharge data and
birth certificates for both deliveries. The study was approved by the Human
Subjects Review Committee at the University of Washington, Seattle, and the
Human Research Review Board at the Washington State Department of Health,
Olympia.
Definitions
Hospitals were classified as level III (providing tertiary care, with
complete perinatal services), level II (with at least 500 births per year,
with board-certified obstetricians and pediatricians on staff, and providing
newborn intermediate care), or level I (having a licensed obstetrical unit,
with fewer than 500 births per year or without one or more level II
criteria).
A delivery was classified as a repeated cesarean delivery without labor if
"repeat cesarean no labor" was checked on the birth certificate and if
labor-related procedure or diagnosis codes of the International
Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM)
7 <http://content.nejm.org/cgi/content/full/345/1/#R7>  were not recorded on
hospital-discharge forms. Labor was considered to have been induced if
"induction of labor" was checked on the birth certificate or if any ICD-9-CM
medical-induction procedure or diagnosis codes were recorded in
hospital-discharge data. Induced labor was classified as induction of labor
with prostaglandins if ICD-9-CM procedure code 96.49 was recorded on the
hospital-discharge form. All other induced labor was classified as induction
of labor without prostaglandins. According to these criteria, there were
6980 women who had repeated cesarean delivery without labor (34.7 percent),
1960 women who had induction of labor without prostaglandins (9.8 percent),
366 women who had induction of labor with prostaglandins (1.8 percent), and
10,789 women who had spontaneous onset of labor (53.7 percent) available for
analysis. Uterine rupture was considered to have occurred if ICD-9-CM
diagnosis code 665.0 or 665.1 was recorded on the hospital-discharge form.
Statistical Analysis
To assess the risk of uterine rupture associated with spontaneous onset of
labor, induction of labor without prostaglandins, and induction of labor
with prostaglandins, as compared with repeated cesarean delivery without
labor, we used Mantel–Haenszel rate ratios to estimate the relative risks
and 95 percent confidence intervals. 8
<http://content.nejm.org/cgi/content/full/345/1/#R8>  Interactions between
the mother's labor status at the second delivery and the type of uterine
incision at the first delivery and the year of the second delivery were
assessed by the likelihood-ratio test, with P values below 0.05 denoting
statistical significance. No significant interactions were found. The
following variables, reported at the time of the second delivery, were
examined for possible confounding effects in all analyses: maternal age;
race or ethnic background; marital status; smoking status during pregnancy;
presence or absence of preexisting diabetes mellitus, chronic hypertension,
moderate-to-severe preeclampsia, and genital herpes; interval between the
deliveries; payer; hospital level; infant birth weight and estimated
gestational age; presence or absence of breech presentation; and presence or
absence of placenta previa. Variables were considered to be confounders if
their inclusion changed the model's relative risk for uterine rupture at the
second delivery associated with any labor-status category by 10 percent or
more. With this criterion, no variables were considered to confound the
models.
Because misoprostol was introduced into obstetrical practice for induction
of labor in Washington in 1996 and has been linked to a higher risk of
uterine rupture, we compared the risk of uterine rupture associated with
prostaglandin-induced labor with that associated with repeated cesarean
delivery without labor, with stratification according to birth year (before
1996 or during 1996). Because prostaglandin induction may be used
differently according to whether there are chronic or perinatal health
conditions — which may, in turn, be independently associated with uterine
rupture — we performed a secondary analysis limited to the 18,419 women
without diabetes mellitus, chronic hypertension, moderate-to-severe
preeclampsia, breech presentation, genital herpes, or placenta previa (91.7
percent). Because a prior vertical uterine cesarean incision may also affect
a woman's risk of uterine rupture, we conducted an analysis limited to the
19,822 women (98.6 percent) without a vertical cesarean uterine incision at
the first delivery. Finally, since the severity of uterine rupture cannot be
determined from diagnostic codes, we examined the frequency of the diagnosis
of selected postpartum complications among women with and without uterine
rupture. Differences between the two groups were compared with use of the
Mantel–Haenszel chi-square test. Because the frequency of postpartum
complications was low, it was not possible to evaluate the relation between
labor status and specific complications of uterine rupture.
Results
Demographic and perinatal characteristics at the time of the second delivery
were similar among women with spontaneous onset of labor and women with no
trial of labor ( Table 1
<http://content.nejm.org/cgi/content/full/345/1/#T1> ). Women who underwent
induction without prostaglandins were more likely than women who did not
have a trial of labor to deliver infants whose estimated gestational age was
more than 42 weeks. Women who underwent prostaglandin induction were less
likely to deliver within two years of their first delivery and more likely
to deliver at a level II hospital than women who had no trial of labor. The
frequency of medical conditions and complications of pregnancy varied
substantially among the groups ( Table 2
<http://content.nejm.org/cgi/content/full/345/1/#T2> ). Women who had
spontaneous onset of labor were significantly less likely than women with no
trial of labor to have diabetes mellitus, chronic hypertension,
preeclampsia, a breech presentation, genital herpes, or placenta previa.
Women with induction without prostaglandins were significantly less likely
than women who did not undergo labor to have breech presentation, genital
herpes, or placenta previa. Finally, women with prostaglandin induction were
significantly less likely to have breech presentation or genital herpes than
women who did not undergo labor.


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[in this window] <http://content.nejm.org/cgi/content/full/345/1/3/T1>
[in a new window] <http://content.nejm.org/cgi/content-nw/full/345/1/3/T1>

Table 1. Characteristics of Second Deliveries among Women with a Prior
Cesarean Delivery, Washington State, 1987 through 1996.



View this table:
[in this window] <http://content.nejm.org/cgi/content/full/345/1/3/T2>
[in a new window] <http://content.nejm.org/cgi/content-nw/full/345/1/3/T2>

Table 2. Medical Conditions and Selected Complications of Pregnancy at the
Time of the Second Delivery among Women with a Prior Cesarean Delivery.

In our study cohort, uterine rupture complicated 4.5 second singleton
deliveries per 1000 (91 women). Uterine rupture occurred at a rate of 1.6
per 1000 among women with repeated cesarean delivery without labor (11
women), 5.2 per 1000 among women with spontaneous onset of labor (56 women),
7.7 per 1000 among women whose labor was induced without prostaglandins (15
women), and 24.5 per 1000 among women with prostaglandin-induced labor (9
women). Women with spontaneous onset of labor were more likely than women
who did not undergo labor to have uterine rupture (relative risk, 3.3; 95
percent confidence interval, 1.8 to 6.0) ( Table 3
<http://content.nejm.org/cgi/content/full/345/1/#T3> ). A greater relative
risk was observed among women with induced labor without prostaglandins
(relative risk, 4.9; 95 percent confidence interval, 2.4 to 9.7), and
particularly those with labor induced by prostaglandins (relative risk,
15.6; 95 percent confidence interval, 8.1 to 30.0). For women giving birth
before misoprostol became generally available in 1996, the relative risk of
uterine rupture associated with prostaglandin-induced labor was 14.1 (95
percent confidence interval, 6.1 to 33.0). The risk was similar among women
who gave birth in 1996 (relative risk, 12.2; 95 percent confidence interval,
3.4 to 39.6). The risk estimates for uterine rupture associated with
spontaneous or induced labor were not materially changed when we excluded
women with diabetes mellitus, chronic hypertension, preeclampsia, breech
presentation, genital herpes, or placenta previa (data not shown). There
were no uterine ruptures among the 272 women with previous vertical
incisions, and the results were unchanged when data on these women were
excluded (data not shown). Women with uterine rupture were significantly
more likely than women without uterine rupture to have postpartum
complications ( Table 4
<http://content.nejm.org/cgi/content/full/345/1/#T4> ).


View this table:
[in this window] <http://content.nejm.org/cgi/content/full/345/1/3/T3>
[in a new window] <http://content.nejm.org/cgi/content-nw/full/345/1/3/T3>

Table 3. Incidence and Relative Risk of Uterine Rupture during a Second
Delivery among Women with a Prior Cesarean Delivery.



View this table:
[in this window] <http://content.nejm.org/cgi/content/full/345/1/3/T4>
[in a new window] <http://content.nejm.org/cgi/content-nw/full/345/1/3/T4>

Table 4. Postpartum Complications of Second Deliveries among Women with a
Prior Cesarean Delivery.

Discussion
In this longitudinal cohort study of 20,095 women whose first delivery of a
singleton child was by cesarean delivery, a trial of labor at the second
delivery was associated with a significant increase in the risk of uterine
rupture. The risk of rupture was increased by a factor of approximately
three in women with spontaneous labor; however, the rate of uterine rupture
among these women was still quite low. The risk of uterine rupture was
highest among women whose labor was induced, particularly when it was
induced by prostaglandins.
Our findings are consistent with the results of two cross-sectional studies,
which demonstrated increased risks of uterine rupture with a trial of labor
in women with prior cesarean section. 1
<http://content.nejm.org/cgi/content/full/345/1/#R1> , 5
<http://content.nejm.org/cgi/content/full/345/1/#R5>  A countrywide study in
Switzerland, which included 92 uterine ruptures, observed a doubling of the
risk among women with a trial of labor, as compared with those who underwent
elective repeated cesarean delivery. 1
<http://content.nejm.org/cgi/content/full/345/1/#R1>  Similar risks were
found in a California cohort analysis that used 1995 statewide
hospital-discharge data, in which 393 uterine ruptures were reported. 5
<http://content.nejm.org/cgi/content/full/345/1/#R5>  One longitudinal
cohort study in Nova Scotia estimated that the relative risk of uterine
rupture associated with a trial of labor, as compared with elective repeated
cesarean delivery, was 5.2, but only 11 women had uterine rupture, and this
increase in risk was not significant. 2
<http://content.nejm.org/cgi/content/full/345/1/#R2>  None of those studies
examined the effect of induction of labor on the risk of uterine rupture
associated with a trial of labor. Three prior case series reported an
increase in uterine rupture among women with prior cesarean delivery in
whose second deliveries labor was induced by prostaglandins. 9
<http://content.nejm.org/cgi/content/full/345/1/#R9> , 10
<http://content.nejm.org/cgi/content/full/345/1/#R10> , 11
<http://content.nejm.org/cgi/content/full/345/1/#R11>  However, these
studies did not include a comparison group of women whose second deliveries
were by cesarean section without labor.
In prior studies, information about a trial of labor was based on
physician-survey or hospital-discharge data alone, and labor status may have
been misclassified. Information in the present study came from linked
birth-certificate and hospital-discharge data — an approach that increases
the accuracy and completeness of data on obstetrical diagnoses and
procedures. 12 <http://content.nejm.org/cgi/content/full/345/1/#R12>  The
use of longitudinally linked maternal data sets also allowed us to use an
entire state's cohort of women with one prior cesarean delivery who had a
second singleton delivery during a 10-year period; this method ensured that
the number of subjects was adequate for the examination of a rare outcome.
Since all levels of hospitals statewide were included, our findings
represent a wide range of hospital settings.
Data derived from vital statistics and administrative records may be limited
in completeness and in the accuracy of coding of obstetrical data. However,
previous research has shown that 99.8 percent of cesarean deliveries are
correctly classified when Washington State linked birth-certificate and
hospital-discharge files are used. 12
<http://content.nejm.org/cgi/content/full/345/1/#R12>  Inaccuracy in the
measurement of exposure is possible, however; a previous study found that
only 72 percent of women with induction of labor were correctly classified
in the Washington State Birth Events Record Database, and no studies have
reported on the accuracy of classification of the other exposure groups. 12
<http://content.nejm.org/cgi/content/full/345/1/#R12>  Nonetheless, because
the recording of labor status is unlikely to depend on uterine-rupture
status, any misclassification would be random and would thus lead to
underestimation of the risk associated with labor. Although we could not
document the accuracy of coding for uterine rupture, the observed rate of
uterine rupture of 4.5 per 1000 among women with prior cesarean delivery was
consistent with the results of other studies (range, 3.2 per 1000 to 6.4 per
1000). 1 <http://content.nejm.org/cgi/content/full/345/1/#R1> , 3
<http://content.nejm.org/cgi/content/full/345/1/#R3> , 5
<http://content.nejm.org/cgi/content/full/345/1/#R5>  Furthermore, the
increased frequency of adverse postpartum complications among women with a
diagnosis of uterine rupture suggests that this diagnosis code was
clinically meaningful.
We did not have information on specific types and dosages of prostaglandin
used, and therefore we could not evaluate the effects of different
preparations. Although the American College of Obstetricians and
Gynecologists currently advises against the use of misoprostol in women with
prior uterine surgery, because of the reported increased frequency of
uterine rupture, this prostaglandin analogue may have been used during 1996,
the last year of our study period. 11
<http://content.nejm.org/cgi/content/full/345/1/#R11> , 13
<http://content.nejm.org/cgi/content/full/345/1/#R13>  However, the
observation that the risk of rupture associated with prostaglandin-induced
labor was increased in the years before misoprostol was available indicates
that this preparation alone could not have been responsible for the
increased risk seen with prostaglandin use.
An increased risk of uterine rupture may be attributed to factors other than
labor status at a second delivery among women with prior cesarean delivery,
and these factors may also influence the decision to undertake a trial of
labor. We restricted our analysis to second singleton births, eliminating
the potentially confounding effects of parity, more than one cesarean
delivery, and multiple gestation, all of which could have predisposed women
both to a scheduled repeated cesarean delivery and to uterine rupture. 14
<http://content.nejm.org/cgi/content/full/345/1/#R14> , 15
<http://content.nejm.org/cgi/content/full/345/1/#R15>  The results were
similar when we excluded data from women with preexisting medical conditions
or complications of pregnancy that might be expected to influence the mode
of delivery and when we excluded data from women with prior vertical
incisions.
At present, the data suggest that induction of labor increases the risk of
uterine rupture among women with one prior cesarean delivery and that labor
induced with use of a prostaglandin confers a greater relative risk. The
overall effect of induction of labor with prostaglandins on uterine rupture
is still unclear and may vary according to the preparation used, the
regimen, and the degree of cervical readiness for induction.
Supported in part by grants from the Agency for Healthcare Research and
Quality (5 T32 HS00034) and from the National Institutes of Health–National
Institute of Nursing Research (T32 NR07039).
We are indebted to Nancy Fugate-Woods, Ph.D., for assistance and comments
and to William O'Brien for data linkage and management support.

Source Information
From the Center for Women's Health Research, Department of Family and Child
Nursing, School of Nursing (M.L.-R.), the Department of Epidemiology, School
of Public Health and Community Medicine (V.L.H.), the Department of
Obstetrics and Gynecology, School of Medicine (T.R.E.), and the Department
of Health Services, School of Public Health and Community Medicine (M.L.-R.,
D.P.M.), University of Washington, Seattle.
Address reprint requests to Dr. Lydon-Rochelle at the Center for Women's
Health Research, Mailstop 357262, University of Washington, Seattle, WA
98195-7262, or at [log in to unmask] <mailto:[log in to unmask]> .
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Vaginal Delivery after Cesarean Section — Is the Risk Acceptable?
 Nearly 40 years ago, Douglas et al. documented the risk of uterine rupture
during a trial of labor after cesarean section. 1
<http://content.nejm.org/cgi/content/full/345/1/#R1>  Among more than 2000
women with scars from prior cesarean sections, uterine rupture occurred
during labor in just over 1 percent, and more than a third of the fetuses in
those cases died. The authors concluded, "Probably the most vehement
objections to the policy of vaginal delivery after cesarean section allude
to the occurrence of catastrophic ruptures of the uterine scar." That
experience, coupled with the mantra "Once a cesarean, always a cesarean,"
cast the practice of vaginal delivery after cesarean section into widespread
disrepute for decades.
Subsequently, the U.S. national cesarean-section rate rose dramatically,
peaking in the late 1980s at nearly 23 percent. This increase attracted
considerable attention, since cesarean sections generally result in greater
short-term and long-term maternal morbidity, maternal mortality, and expense
than vaginal deliveries. A third of the cesarean sections were elective
repeated procedures, with absolute numbers rising as the rate of primary
cesarean section rose.
An obvious way to curb the rising cesarean-section rate was to revive the
practice of vaginal delivery after cesarean section. Enthusiastic reports of
success 2 <http://content.nejm.org/cgi/content/full/345/1/#R2> , 3
<http://content.nejm.org/cgi/content/full/345/1/#R3>  and an optimistic
meta-analysis that found no increase in perinatal mortality with a trial of
labor 4 <http://content.nejm.org/cgi/content/full/345/1/#R4>  propelled the
juggernaut. Insurers initiated programs to promote vaginal delivery after
cesarean section and to educate doctors and patients regarding its benefits.
Some insurers even felt justified in refusing to pay for repeated cesarean
sections that were not preceded by attempts at vaginal delivery. Individual
physicians, and to some extent their professional organizations, were
cajoled or coerced into supporting these programs, lest they be dropped from
the roster of providers or portrayed as uncooperative and nonprogressive. As
experience again accumulated, however, so too did reports of maternal and
perinatal morbidity and mortality associated with vaginal delivery after
cesarean section; most of these adverse effects were attributable to uterine
rupture. 5 <http://content.nejm.org/cgi/content/full/345/1/#R5> , 6
<http://content.nejm.org/cgi/content/full/345/1/#R6>  Efforts to improve the
safety of vaginal delivery after cesarean section have focused on attempts
to identify risk factors for uterine rupture. Recent investigations into the
effects of oxytocic agents have yielded inconsistent results without a clear
message. 7 <http://content.nejm.org/cgi/content/full/345/1/#R7> , 8
<http://content.nejm.org/cgi/content/full/345/1/#R8> , 9
<http://content.nejm.org/cgi/content/full/345/1/#R9>
In this issue of the Journal, Lydon-Rochelle et al. report on a study in
which they used a large statewide data base of more than 20,000 women in
Washington State to examine the risk of uterine rupture associated with
various modes of delivery and induction of labor. 10
<http://content.nejm.org/cgi/content/full/345/1/#R10>  All the women had
undergone one previous cesarean section and were delivering a second
singleton baby. The overall risk of uterine rupture was 4.5 per 1000, which
is consistent with rates in other studies. 7
<http://content.nejm.org/cgi/content/full/345/1/#R7> , 8
<http://content.nejm.org/cgi/content/full/345/1/#R8> , 9
<http://content.nejm.org/cgi/content/full/345/1/#R9>  The rate of uterine
rupture associated with spontaneous onset of labor was 5.2 per 1000 and that
associated with induction of labor without prostaglandins was 7.7 per 1000.
These rates were significantly higher than the 1.6 per 1000 among women who
had repeated cesarean sections without labor, but not significantly
different from one another. Most striking was the rate of uterine rupture,
24.5 per 1000, when labor was induced with a prostaglandin.
Previous reports of two small, uncontrolled case series 11
<http://content.nejm.org/cgi/content/full/345/1/#R11> , 12
<http://content.nejm.org/cgi/content/full/345/1/#R12>  suggested that a 5 to
10 percent risk of uterine rupture was associated with use of misoprostol, a
highly potent synthetic prostaglandin E1 analogue, to induce labor. The
American College of Obstetricians and Gynecologists subsequently warned
against the use of misoprostol for this purpose. 13
<http://content.nejm.org/cgi/content/full/345/1/#R13>  Although
Lydon-Rochelle et al. did not have information about the prostaglandin
preparations used to induce labor in the women in their cohort, they
performed an analysis with stratification according to year to look
specifically at deliveries before and after 1996, when misoprostol began to
be widely used. They found that the risk associated with the use of a
prostaglandin to induce labor was similar during the two periods, suggesting
that the risk is not limited to misoprostol but extends to other
prostaglandin preparations as well.
The 91 women in the study by Lydon-Rochelle et al. who had uterine ruptures
had substantially greater rates of several postpartum complications,
suggesting that these ruptures were clinically important and not merely
instances of asymptomatic dehiscence. Notably, the incidence of infant death
was 10 times as high among the 91 women who had uterine rupture as among the
20,004 who did not (5.5 percent vs. 0.5 percent). It is important to
emphasize that this study, like all others to date, was an observational
study of the results of clinical practice and not a randomized trial.
The relative risk of 3.3 in the present study for uterine rupture in women
with a spontaneous onset of labor, as compared with those who underwent
elective repeated cesarean section, is consistent with the odds ratio of 2.1
for a similar comparison reported in a recent meta-analysis of 11 studies
involving a total of 39,000 subjects. 14
<http://content.nejm.org/cgi/content/full/345/1/#R14>  This meta-analysis
also found significant increases in the risks of fetal death (odds ratio,
1.7) and of an Apgar score of less than 7 at five minutes (odds ratio, 2.2)
associated with a trial of labor as compared with elective repeated cesarean
delivery. These risk estimates reflect broad experience in a wide range of
clinical-practice settings. There is no reason to believe that improvements
in clinical care can substantially reduce the risks of uterine rupture and
perinatal mortality.
Given the potential risks, why might a woman choose a trial of labor? Women
who successfully deliver vaginally generally have less postpartum
discomfort, shorter hospital stays, and shorter periods of disability than
women who undergo repeated cesarean section. A trial of labor may be
associated with a lower risk of fever than elective repeated cesarean
section. 14 <http://content.nejm.org/cgi/content/full/345/1/#R14>  Women who
plan future pregnancies may prefer to avoid repeated cesarean deliveries
that further increase the risks of uterine rupture, placenta accreta, and
morbidity related to multiple abdominal surgeries. Finally, there may be
social and cultural reasons why some women prefer vaginal delivery.
Slovic recognized that "experts" (such as health care policy analysts,
public health officials, and insurance company executives) perceive risk
differently from laypeople (patients). 15
<http://content.nejm.org/cgi/content/full/345/1/#R15>  Experts judge risk
according to technical estimates of numbers of deaths. The rate of perinatal
death, for example, is 5.8 per 1000 with trials of labor after cesarean
section, as compared with 3.4 per 1000 with elective repeated cesarean
section. 14 <http://content.nejm.org/cgi/content/full/345/1/#R14>  The
absolute difference between them is 2.4 per 1000 (or 1 per 417), a
relatively small number. Patients are more apt to judge risk according to
the degree to which they "dread" the unwanted outcome. "Dread," in turn, is
determined by the degree to which the outcome is irreversible, potentially
lethal, and uncontrollable. By these criteria, the possibility of perinatal
death resulting from a trial of labor would probably be associated with a
high degree of dread.
The process of obtaining informed consent for medical care requires that
physicians provide patients with the information that a reasonable person
would want under the circumstances. Most reasonable women considering a
trial of labor after a prior cesarean delivery would want to know that
spontaneous labor is associated with a tripling of the risk of uterine
rupture and that induction of labor with prostaglandins is associated with
an increase in that risk by a factor of 15. Should a rupture occur, the risk
of perinatal mortality increases by a factor of 10. Some reasonable persons
may conclude that these absolute risks are so small that they are worth
taking and are outweighed by the benefits of a successful vaginal birth.
Nonetheless, these issues must be discussed with each patient, and she must
make that decision for herself. After a thorough discussion of the risks and
benefits of attempting a vaginal delivery after cesarean section, a patient
might ask, "But doctor, what is the safest thing for my baby?" Given the
findings of Lydon-Rochelle et al., my unequivocal answer is: elective
repeated cesarean section.

Michael F. Greene, M.D.
Massachusetts General Hospital
Boston, MA 02114
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Edward E. Rylander, M.D.
Diplomat American Board of Family Practice.
Diplomat American Board of Palliative Medicine.