Risk of Perinatal Death Associated With Labor After Previous
Cesarean Delivery in Uncomplicated Term Pregnancies
Gordon C. S. Smith, MD, PhD; Jill P. Pell, MD; Alan D. Cameron, MD;
Richard Dobbie, BSc
Context Trial of labor after previous cesarean delivery is associated with
increased risk of uterine rupture. However, no reliable data exist on the
effect of a trial of labor on the risk of perinatal death in otherwise
uncomplicated term pregnancies.
Objective To determine the risk of intrapartum stillbirth or neonatal death
not related to congenital abnormality among women with uncomplicated term
pregnancies who had a trial of labor after previous cesarean delivery, compared
with women having a planned repeat cesarean delivery, and multiparous and
nulliparous women at term not delivered by planned cesarean method.
Design and Setting Population-based, retrospective cohort study of data from the
linked Scottish Morbidity Record and Stillbirth and Neonatal Death Enquiry
encompassing births in Scotland between January 1, 1992, and December 31, 1997.
Population A total of 313 238 singleton births between 37 and 43 weeks'
gestational age in which the fetus was in a cephalic presentation.
Main Outcome
Measure Delivery-related
perinatal death, defined as intrapartum stillbirth or neonatal death unrelated
to congenital anomaly, compared among the 4 groups.
Results Among women who had a trial of labor following previous cesarean
delivery (n = 15 515), the overall rate of delivery-related perinatal
death was 12.9 (95% confidence interval [CI], 7.9-19.9) per 10 000 women.
This was approximately 11 times greater (odds ratio [OR], 11.6; 95% CI,
1.6-86.7) than the risk associated with planned repeat cesarean delivery (n =
9014), more than twice (OR, 2.2; 95% CI, 1.3-3.5) the risk associated with
other multiparous women in labor (n = 151 549), and similar to the risk
among nulliparous women in labor (n = 137 160; OR, 1.3; 95% CI, 0.8-2.1).
The associations were not explained by differences in maternal height, smoking
status, socioeconomic status, age, fetal growth, or week of gestation at
delivery. Among women having a trial of labor, the rate of death due to
mechanical causes, including uterine rupture, was 4.5 (95% CI, 1.8-9.3) per
10 000 women. This was more than 8 times greater than other multiparous
women (OR, 8.5; 95% CI, 3.2-22.3) and nulliparous women (OR, 8.8; 95% CI,
3.2-24.2).
Conclusions The absolute risk of perinatal death associated with trial of
labor following previous cesarean delivery is low. However, in our study, the
risk was significantly higher than that associated with planned repeat cesarean
delivery, and there was a marked excess of deaths due to uterine rupture
compared with other women in labor.
JAMA. 2002;287:2684-2690
Increasing rates of cesarean delivery are a
major cause for concern in almost all developed countries.1 A number of strategies
have been proposed that aim to reduce the overall proportion of cesarean
deliveries, including trial of labor after previous cesarean deliveries.2 Observational studies3, 4 suggest that trial of
labor is associated with a significantly increased risk of uterine rupture. A
meta-analysis reported an increased risk of perinatal death associated with
trial of labor5 but included
premature births between 28 and 36 weeks' gestation and breech deliveries.6 There is no
large-scale study of the relative and absolute risks of perinatal death among
women previously delivered by cesarean method but with an uncomplicated
pregnancy at term. In the present study, we sought to address this by linking
national registers of pregnancy discharge data and perinatal deaths.
The analysis was designed to determine the risk
of intrapartum stillbirth or neonatal death unrelated to congenital abnormality
among women with an uncomplicated term pregnancy who had a trial of labor
following at least 1 previous cesarean delivery. Trial of labor was defined as
any vaginal or emergency (unplanned) cesarean delivery occurring at or beyond
37 weeks' gestation in a woman who had previously been delivered by cesarean
method. These women were compared with 3 groups: (1) women having planned
repeat cesarean delivery, (2) other multiparous women at term not delivered by
planned cesarean method, and (3) nulliparous women at term not delivered by
planned cesarean method. Nulliparous women were women with no previous
pregnancies or whose previous pregnancies all ended in abortion.
Population
The Scottish Morbidity Record (SMR2) collects information on clinical and
demographic characteristics and outcomes for all patients discharged from
Scottish maternity hospitals. The register is subjected to regular quality
assurance checks and has been more than 99% complete since the late 1970s.7 An analysis of 1414
records from 1996 through 1997 demonstrated that the register was free of
significant errors in more than 98% of records in all the fields used in the
present analysis, with the exception of postcode (94.0%), height (96.2%),
estimated gestation (94.4%), and method of induction of labor (93.6%) (Jim
Chalmers, MBChB, Information and Statistics Division, National Health Service,
Edinburgh, Scotland, written communication, April 2001). The SMR2 records were
linked to records from the Scottish Stillbirth and Neonatal Death Enquiry. This
national register has routinely classified all perinatal deaths in Scotland
since 1983. It is almost 100% complete and has been described in detail
elsewhere.8
Study Group
The study group consisted of all births in Scotland between January 1, 1992,
and December 31, 1997. The exclusion criteria for the study group were multiple
pregnancy, noncephalic presentation, delivery outside the range of 37 to 43
weeks' gestation, perinatal deaths due to congenital anomaly, antepartum
stillbirth not due to congenital anomaly, and deliveries by planned cesarean
method, except among women who had been delivered by cesarean method in a
previous pregnancy.
The main outcome of this study was
delivery-related perinatal death, defined as intrapartum stillbirth or neonatal
death not caused by congenital anomaly. Stillbirths were defined as newborns
that showed no signs of life following delivery. Stillbirths were subdivided
into antepartum (deaths before the onset of labor) and intrapartum (deaths
during labor). Neonatal death was defined as death during the first 4 weeks of
life in a live newborn. Deaths caused by congenital anomaly were defined as any
structural or genetic defect incompatible with life or potentially treatable
but causing death.
In the comparison of risk of perinatal death among
groups of women, the following factors were considered as possible confounders:
socioeconomic deprivation, smoking, maternal age, maternal height, gestational
age, and birth weight. Postcode of residence was used to derive Carstairs
socioeconomic deprivation scores.9 These are based on
1991 census data on car ownership, unemployment, overcrowding, and social class
within postcode sectors of residence that contain, on average, approximately
1600 residents. The deprivation scores were then used to categorize women into
quintiles of socioeconomic deprivation within the study cohort. Higher
quintiles indicate a greater degree of deprivation. Smoking was defined as the
smoking status of the woman at the time of first attendance for antenatal care.
Maternal age was defined as the age of the mother at the time of birth.
Maternal height was measured in centimeters, and the value used was that
documented in each woman's clinical record. Height is generally measured using
a free-standing or wall-mounted height measure. Gestational age at birth was
defined as completed weeks of gestation on the basis of the estimated date of
delivery in each woman's clinical record. Gestational age has been confirmed by
ultrasound in the first half of pregnancy in more than 95% of women in the
United Kingdom since the early 1990s.10 Birth weight was
categorized into sex- and gestational age-specific deciles, using a method
previously described in detail.11 Low birth weight was
defined as birth weight of less than 2500 g.
The cause of perinatal death was classified
according to a hierarchical system that is described in detail elsewhere.12 Deaths were initially
classified according to the following direct obstetric causes (in order):
toxemia, hemorrhage, mechanical, maternal, and none of these obstetric causes.
Mechanical was defined as death from uterine rupture, cord compression
(including prolapse), birth trauma, or asphyxia associated with disproportion.
In the absence of any of the listed direct obstetric causes, the deaths were
classified by the pediatric diagnoses and these were grouped into intrapartum
anoxia, other (pulmonary causes, intracranial hemorrhage, infection, other
hemorrhage, and miscellaneous), and unexplained. The hierarchy dictates that a
perinatal death where there was severe preeclampsia complicated by abruption
would be classified as being due to toxemia because toxemia is above both
hemorrhage and intrapartum anoxia in the hierarchy.
Statistical Analyses
Continuous variables were summarized by the median and interquartile range, and
comparisons between groups were performed using the Mann-Whitney U test. Univariate comparisons of
dichotomous data were performed using the 2 test (>5 observations in all cells) or Fisher
exact test (5 observations in 1 cells). Ordinal data
were compared using the 2 test
for trend. The P values for all
hypothesis tests were 2-sided and .05 was the significance level. Adjusted
rates were obtained using direct standardization. Crude and adjusted odds
ratios (ORs) were obtained using logistic regression analysis. Cases with
missing values were excluded from the multivariate analysis. The statistical
significance of interaction terms was assessed using the likelihood ratio test.
Model goodness-of-fit was assessed using the Hosmer-Lemeshow test based on
deciles of probability.13 All statistical
analyses were performed using version 7.0 of the Stata software package (Stata
Corp, College Station, Tex).
Of the SMR2 records with a perinatal death
documented, 97.8% could be linked to a corresponding record in the Stillbirth
and Neonatal Death Enquiry. From 1992 through 1997, there were 356 958
records of singleton births in Scotland in the SMR2 database. Among these
records, there were 697 (0.2%) with missing values for gestational age, 4873
(1.4%) with missing values for presentation at delivery, and 8 (<0.1%) with
missing values for number of previous cesarean deliveries. A total of 5564
records had 1 or more missing values, leaving 351 394 records. Among this
group, there were 16 427 fetuses (4.7%) with a noncephalic presentation,
621 perinatal deaths (0.2%) related to congenital anomaly, 1479 antepartum
stillbirths (0.4%) unrelated to congenital anomaly, 20 628 births (5.9%)
outside the range of 37 to 43 weeks' gestational age, and 9827 births (2.8%) by
planned cesarean method where the women had not had a previous cesarean
delivery. A total of 38 156 records had 1 or more exclusion criteria,
resulting in a study group of 313 238 (87.8% of all singleton births
during the study period).
The study group was subdivided into 15 515
women previously delivered by cesarean method who had a trial of labor, 9014
women who had previously been delivered by cesarean method who delivered by
planned cesarean method in the current pregnancy, 137 160 nulliparous
women who were not delivered by planned cesarean method, and 151 549
multiparous women who had not had a previous cesarean delivery and did not
deliver by planned cesarean method in the current pregnancy. Within the study
group, there were missing values for maternal height in 26 825 women
(8.6%), for smoking status in 29 730 (9.5%), for deprivation quintile in
4 975 (1.6%), for birth weight in 61 (<0.1%), and for 5-minute Apgar
score in 36 (<0.1%).
The study group characteristics and basic
outcome data are given in Table 1.
The highest rate of perinatal death (12.9 per 10 000 women) was seen among
women having a trial of labor (Table 2).
The risk of a delivery-related perinatal death among women having a trial of
labor was more than 11 times (OR, 11.6; 95% confidence interval [CI], 1.6-86.7)
that of women having a planned repeat cesarean delivery (Table 3).
The risk of death associated with a trial of labor was similar when compared
with nulliparous women in labor (OR, 1.3; 95% CI, 0.8-2.1) but was more than
twice that of other multiparous women in labor (OR, 2.2; 95% CI, 1.3-3.5). When
delivery-related perinatal deaths among all women who had previously been
delivered by cesarean method were analyzed, it was estimated that 91% (95% CI,
36%-99%) could be attributed to the increased risk of death associated with a
trial of labor.
Statistical comparison with the planned repeat
cesarean delivery group was problematic because there was only a single death
among the 9014 women. All the records with missing values were among the 9013
survivors and, therefore, excluding missing records resulted in a weaker
association between trial of labor and perinatal death compared with planned
repeat cesarean delivery simply by reducing the denominator in the latter group
(Table 3).
However, among the cases with nonmissing values, adjusting for maternal age,
smoking status, height, deprivation quintile, gestational age at birth, and
birth weight decile strengthened the association between trial of labor and
perinatal death when compared with elective repeat cesarean delivery (OR, 11.7;
95% CI, 1.4-101.6). When women having a trial of labor were compared with nulliparous
and other multiparous women, adjusting for maternal age, smoking status,
height, deprivation quintile, gestational age at birth, and birth weight decile
had no effect on the ORs (Table 3).
When the analyses were confined to births at or
after 40 weeks' gestation, the results were similar (Table 2).
Although there were no deaths among the 1064 planned repeat cesarean deliveries
at or after 40 weeks' gestation, the numbers were too small to be statistically
significantly lower than the trial of labor group. Among births at or after 40
weeks' gestation, the risk of death associated with a trial of labor was
similar when compared with nulliparous women in labor (OR, 1.2; 95% CI,
0.6-2.2) but higher when compared with other multiparous women in labor (OR,
2.7; 95% CI, 1.4-5.2).
Among women previously delivered by cesarean
method, 369 (2.4%) of those having a trial of labor had more than 1 previous
cesarean delivery, whereas 2962 (32.9%) of those delivered by planned cesarean
method had more than 1 previous cesarean delivery. Of the 20 perinatal deaths
among women having a trial of labor, 19 women (95%) had only 1 previous
cesarean delivery. Among women previously delivered by cesarean method, 5206
(33.6%) of those having a trial of labor had previously had a vaginal birth,
whereas 988 (11.0%) of those delivered by planned cesarean method had
previously had a vaginal birth. Of the 20 perinatal deaths among women having a
trial of labor, 5 women (25%) had previously had a vaginal birth. Among the
trial of labor group, there were 12 perinatal deaths among 3945 neonates born
by emergency cesarean delivery and 8 deaths among 11 570 neonates
delivered vaginally (P = .001).
The rates of perinatal death due to different
causes differed among the 4 groups (Table 4).
Compared with other multiparous women, women having a trial of labor had more
than 8 times the risk of a perinatal death due to a mechanical cause (OR, 8.5;
95% CI, 3.2-22.3) and almost 3 times the risk of a perinatal death due to
intrapartum anoxia (OR, 2.8; 95% CI, 1.3-6.5). When compared with nulliparous
women, women having a trial of labor had an increased risk of perinatal death
due to mechanical causes alone (OR, 8.8; 95% CI, 3.2-24.2).
Women undergoing a trial of labor were less
likely to have a prostaglandin E2 (PGE2) induction, had
shorter labors, had lower rates of operative vaginal delivery, and had higher
rates of emergency cesarean delivery than nulliparous women (Table 5).
Women undergoing a trial of labor were more likely to have a PGE2
induction, had longer labors, and had higher rates of both operative vaginal
and cesarean delivery than other multiparous women. Among women having a trial of
labor, there were 3 perinatal deaths among 2395 women induced with PGE2
and 17 deaths among 13 120 women not treated with PGE2 (P>.99).
In addition to the 15 515 women who
fulfilled the criteria for trial of labor at term, there were 35 women who
fulfilled the same criteria except that the newborn was an antepartum
stillbirth not caused by congenital abnormality at term. Fifteen of these women
delivered before 39 weeks, 10 delivered in the 39th week of gestation, and 10
delivered at or after 40 weeks' gestation.
The ideal means to determine the risks and
benefits of trial of labor vs planned repeat cesarean delivery would be a
randomized controlled trial. In practice, this would be difficult to perform
because many women would be unhappy to have such a decision made in a random
manner and large numbers of women would be required for a study powered to
detect differences in such rare outcomes as uterine rupture and perinatal
death. In the absence of randomized controlled trial evidence, analysis of
observational data must be used to estimate the risks of these rare outcomes. A
recent observational study4 has reported on the
relative and absolute risks of uterine rupture associated with trial of labor.
Herein, we report the risk of perinatal death associated with trial of labor
among women at term with a singleton pregnancy in a cephalic presentation.
In the present study, the risk of
delivery-related perinatal death among women having a trial of labor was more
than 11 times that of women having a planned repeat cesarean delivery. Women
having a planned repeat cesarean delivery experienced the lowest death rate
among any of the groups. The low rate of death was explained by the absence of
any risk of intrapartum stillbirth and a significantly lower risk of neonatal
death. The risk associated with planned repeat cesarean delivery at term was so
low that only a single death occurred in Scotland during the 6 years of the
study period. Multivariate statistical comparison among groups is problematic
when the number of events is so small, and larger studies will be required to
analyze adequate numbers of deaths following planned cesarean delivery.
However, selection bias is unlikely to explain the lower risk of death among
women having a planned repeat cesarean delivery, because they are more likely
to have medical and obstetric complications than women offered a trial of
labor.4 Consistent with
this, adjusting for maternal age, smoking status, height, deprivation quintile,
gestational age at birth, and birth weight decile for gestational age
strengthened the association between trial of labor and perinatal death when
compared with women having a planned repeat cesarean delivery, though the CIs
were wide because of the small number of cases.
Our observed rate of perinatal death associated
with planned repeat cesarean delivery, 1.1 per 10 000 women, is much lower
than previously cited.5 However, previously
published perinatal mortality figures for both trial of labor and planned
cesarean delivery did not exclude breech presentations and preterm newborns
delivered between 28 and 36 weeks' gestation.6 Since prematurity and
breech presentation are associated with an excess of perinatal mortality,14, 15 these data are unhelpful
in informing women who reach term with a fetus presenting cephalically. This
group accounted for 84% of women with a previous cesarean delivery in our
study.
When compared with other multiparous women in
labor, women having a trial of labor had approximately twice the rate of
delivery-related perinatal death. This finding was due to an increased risk of
death due to mechanical causes, including uterine rupture, and death due to
intrapartum anoxia not related to uterine rupture. The overall rate of delivery-related
perinatal death among women having a trial of labor was not significantly
greater than nulliparous women in labor. The increased number of deaths due to
mechanical causes among women having a trial of labor compared with nulliparous
women was offset by a lower rate of death due to other causes. The observation
that the level of risk of nonmechanical perinatal death among women having a
trial of labor was intermediate between other multiparous and nulliparous women
probably reflects the fact that approximately one third of women having a trial
of labor had previously had a vaginal birth. There are other possible factors
that could contribute to differences in outcome among the groups that were not
recorded in the database, such as epidural anesthesia, use of electronic fetal
monitoring, and details of maternal medical and obstetric complications.
Further studies will be required to determine whether systematic variation in
any of these variables may contribute to differences in the risk of delivery-related
perinatal death among these groups.
The data presented in this article are collected
nationally and form an extract of a larger data set, which is reported in
detail elsewhere.12 Overall, the
statistics were comparable with previous analyses of perinatal deaths. The
overall rate of intrapartum stillbirth unrelated to congenital abnormality of
2.5 per 10 000 births was comparable with previous studies from
Scandinavia,16 and the total
proportion of all stillbirths that were classified as intrapartum was 11%,
which is similar to national data from England.17 The number of
neonatal deaths observed in our study was lower than a report from Wales,18 which described 7.4
neonatal deaths attributable to an intrapartum event per 10 000 births.
However, that study included neonates of all gestational ages, using a
birth-weight cutoff of more than 1499 g, which would have included a
significant proportion of preterm births.
Current recommendations are that planned
cesarean delivery should be performed in the 39th week of gestation to reduce
the risk of neonatal respiratory morbidity.19 It could be argued
that uterine rupture may occur in earlier weeks of gestation and that the
apparent protective effect of planned cesarean delivery is exaggerated.
However, 85% of delivery-related perinatal deaths at term among women having a
trial of labor occurred at or after 39 weeks' gestation. This is consistent
with the observation that approximately 15% of multiparous women will undergo
labor between the start of the 37th week and the start of the 39th week of
gestation.20 Therefore, it
seems likely that most deaths could have been avoided by planned cesarean
delivery at the start of the 39th week of gestation. Moreover, planned cesarean
delivery at this time would also avoid exposure to the risk of antepartum
stillbirth while awaiting the onset of labor. There were 20 antepartum
stillbirths among women having a trial of labor at or after 39 weeks' gestation
and a proportion of these may also have been prevented by planned cesarean
delivery at the start of the 39th week of gestation. Therefore, the potential
protective effect on perinatal death of planned cesarean delivery over trial of
labor may be greater than estimated in the present study of intrapartum
stillbirths and neonatal deaths.
The definition of a trial of labor used in this
study was that a woman who had previously been delivered by cesarean method was
delivered at term by a method other than planned cesarean. However, it is
likely that a small proportion of these women were due to have a planned
cesarean delivery but presented in labor before their scheduled date and an
emergency cesarean delivery was performed in early labor. Moreover, the
database did not include information on the nature of the incision used in the
previous cesarean delivery. For this reason, we repeated the analysis confined
to births at or after 40 weeks' gestation. By this time, all women scheduled
for planned cesarean delivery should have had the procedure, including any
women who had previously had a classic cesarean delivery. The risks of
perinatal death were virtually unchanged, suggesting that our results are
robust. The outcome of trial of labor was comparable with previous studies: 75%
had a vaginal delivery, which was almost identical to an analysis of more than
17 000 trials of labor from Switzerland.6
Our data provide essential information for women
to make an informed choice about a trial of labor. Overall, the point estimate
of the risk of a perinatal death associated with a trial of labor is 1 in 775,
and the 95% CIs indicate that the risk is unlikely to be higher than 1 in 500.
The point estimate of the risk of a perinatal death due to uterine rupture
associated with a trial of labor is 1 in 2200, and the 95% CIs indicate that
the risk is unlikely to be higher than approximately 1 in 1000.
Considerable caution should be applied when
extrapolating these data to considering possible benefits of planned cesarean
delivery among women who have not previously had a cesarean birth. More than
one third of delivery-related perinatal deaths among multiparous women who had
not previously been delivered by cesarean method were observed before 39 weeks
of gestation. Scheduling planned cesarean delivery for the start of the 39th
week of gestation may have failed to prevent many of these deaths. Moreover, we
present no data on the risk of perinatal death following planned cesarean
delivery among nulliparous women.
Obstetricians have faced pressure from
government and health care insurers to advocate vaginal birth after cesarean
delivery as one strategy to reduce the overall rate of cesarean delivery.
However, this pressure has been exerted in the absence of any reliable
information on the risks to the newborn for most women. This study is the first
to our knowledge that is adequately powered and analyzed to provide information
on the risks of perinatal death associated with the management of women with a
history of cesarean delivery but an otherwise uncomplicated pregnancy at term.
Author/Article Information
Author Affiliations: Department of
Obstetrics and Gynaecology, Cambridge University, Cambridge, England (Dr
Smith); Department of Public Health, Greater Glasgow Health Board (Dr Pell),
and Department of Fetal Medicine, The Queen Mother's Hospital (Dr Cameron),
Glasgow, Scotland; and Information and Statistics Division, Common Services
Agency, Edinburgh, Scotland (Mr Dobbie).
Corresponding Author and Reprints:
Gordon C. S. Smith, MD, PhD, Department of Obstetrics and Gynaecology,
Cambridge University, Rosie Maternity Hospital, Cambridge, CB2 2QQ, England
(e-mail: [log in to unmask]).
Author Contributions: Study concept and design:
Smith, Pell.
Acquisition of data: Pell, Dobbie.
Analysis and interpretation of
data: Smith, Pell, Cameron.
Drafting of the manuscript: Smith, Pell.
Critical revision of the
manuscript for important intellectual content: Smith, Pell, Cameron, Dobbie.
Statistical expertise: Smith, Pell.
Administrative, technical, or
material support: Smith, Pell, Cameron,
Dobbie.
Study supervision: Smith.
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Edward E.
Rylander, M.D.
Diplomat American
Board of Family Practice.
Diplomat American
Board of Palliative Medicine.