Summary of 4 Studies on VBAC safety
-by Gretchen
Humphries, MS, DVM
The purpose of this paper is to provide a simple
summary of the 4 largest and most recent studies
done on vaginal birth after cesarean (VBAC) and
elective repeat cesarean (ERC).
Because complications associated with any form
of birth are rare events, large numbers of births
must be studied to gain an accurate measure of
those complications. It is important to not rely
on interpretation of opinion when making a decision
about VBAC, but rather to assess the available
data and make an informed decision based on fact,
not emotion. While I have very strong opinions
about the inherent flaws, and even dangers represented
by the medical model of obstetrical care, the
fact is that most women plan births within that
system. Therefore, it is appropriate to look at
the information provided by that system.
There are serious flaws in all of these studies;
flaws that may over-estimate the risks specifically
associated with VBAC. Nevertheless, the results
of these studies still support VBAC as a safe
and reasonable choice for most women. Uterine
rupture is the one obstetrical complication that
is most popularly associated with VBAC trials
of labor (TOL) and as such, is often used to discourage
VBAC TOLs, in spite of its rarity. While these
studies do not accurately assess the risk of uterine
rupture in a completely unmedicated VBAC (there
are no published studies that do so), they probably
do accurately assess the risk involved in a typical
hospital VBAC as managed by an obstetrician.
Study 1
"Risk of Uterine Rupture During Labor
Among Women With a Prior Cesarean Delivery"
Lyndon-Rochelle M., Holt V.L., Easterling T.R.,
Martin D.P. NEJM Vol. 345, 3-8 July 5, 2001.
20,095 women with 1 prior cesarean section comprised
the study group. They each gave birth to a live,
single infant between 1987 and 1996.
Uterine rupture
Elective repeat cesarean (ERC) with no labor:
0.16% (11 of 6980)
Spontaneous Onset of Labor (SOOL): 0.52% (56
of 10,789)
Induction of Labor without Prostaglandin: 0.77%
(15 of 1960)
Induction of Labor with Prostaglandin: 2.45%
(9 of 366)
The overall risk of uterine rupture in all TOL
groups was 0.6% (80 of 13115)
There was no information given about augmentation
of labor in any of the groups that labored.
Complications such as diabetes mellitus, chronic
hypertension, preeclampsia, breech presentation,
genital herpes or placenta previa were not associated
with a higher risk of uterine rupture. Likewise,
prior lower vertical incision was not associated
with an increased risk of uterine rupture.
Fetal Deaths
There were 5 fetal deaths in the women that had
uterine ruptures (91 total ruptures). The authors
didn’t report which specific groups were
involved. There were 100 fetal deaths in the women
that did not have uterine ruptures (20,004 total).
If all of the uterine rupture associated deaths
occurred in the groups of women that labored,
then the risk of the baby dying as a result of
a uterine rupture associated with TOL is 0.04%
(5 of 13115), over 10 times less than the risk
of the baby dying for any other reason (0.5% or
100 of 20,004).
Conclusion from the study
"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."
Study 2
"Elective repeat cesarean delivery versus
trial of labor: A meta-analysis of the literature
from 1989 to 1999" Mozerkewich, EL and Hutton
EK. Am J Obstet Gynecol Vol. 183, 1187-1197, Nov.
2000
The authors of this study searched MEDLINE and
EMBASE databases for all English language published
reports, between 1989 and 1999, on VBAC, TOL,
trial of scar (TOS) and uterine rupture. They
selected a total of 15 studies that were of a
quality and make-up to be appropriate for meta-analysis
– they pooled the data from each individual
study together and re-analysed the data as a whole,
as appropriate for each item they were analyzing.
They analyzed for uterine rupture, maternal mortality,
fetal or neonatal mortality, low APGAR score,
maternal transfusion and hysterectomy. Uterine
rupture was defined as symptomatic, requiring
surgical repair or involved extrusion of fetal
parts. All women who chose ERC were eligible for
a TOL and opted for surgery instead.
28,813 women attempted VBAC with 20,746 achieving
a vaginal birth (72.3%).
Uterine Rupture
TOL (trial of labor) group: uterine rupture rate
was 0.4% (4 of 1000)
ERC (elective repeat cesarean) group: uterine
rupture rate of 0.2% (2 of 1000)
Maternal Deaths and Complications
There were 3 maternal deaths among 27,504 women
in the TOL group. All 3 women were undergoing
a repeat cesarean after TOL. There were no maternal
deaths among 17,740 women undergoing an ERC. The
difference between the 2 groups was not statistically
significant.
Maternal febrile morbidity (fever) was less frequent
among women in the TOL group. This was significant
across all the studies that looked at this complication.
Need for a transfusion was significantly less
among women in the TOL group. This was significant
across all the studies that looked at this complication.
Need for a hysterectomy was significantly less
in the TOL group in all but 1 study, which found
no difference between TOL and ERC groups.
Fetal Deaths and Complications
Deaths due to intrauterine death before labor,
lethal birth defects and prematurity were excluded.
TOL births: 0.2% (38 of 19,842).
ERC births: 0.1% (10 of 13,292).
There was no way to determine the actual cause
of any of these deaths, so no conclusions can
be drawn as to the impact uterine rupture may
or may not have had, as opposed to other obstetrical
conditions and interventions.
5-minute APGAR <7 was more common in the TOL
group but this was statistically significant in
only 2 of 7 studies that were used for this comparison.
Facts of note
Between 693 and 3332 women would need to undergo
ERC to prevent a single fetal or neonatal death
attributable to TOL.
Between 374 and 809 women would need to undergo
ERC to prevent a single case of uterine rupture.
Conclusion from the study
"Our findings suggest that small increases
in the uterine rupture rate and in fetal and neonatal
mortality rates may result from a trial of labor
with respect to elective repeat cesarean delivery.
These increases may be counterbalanced by reductions
in maternal morbidity with a trial of labor, including
febrile morbidity, transfusion, and hysterectomy.
Either a trial of labor or elective repeat cesarean
delivery may be a reasonable option for women
with at least one previous cesarean delivery."
Study 3
"Vaginal Birth After Cesarean and Uterine
Rupture Rates in California" Gregory KD,
Korst, LM, Cane P, Platt, LD, Kahn, K. Obstet
& Gynecol Vol.94, 985-989, Dec. 1999
This study looked at the hospital discharge data
for 536,785 women who gave birth in California
in the year 1995.
The overall cesarean rate that year was 20.8%
(111,374 of 536,785)
Women who had previous cesarean(s) were 12.5%
(66,856 of 536,785) of the study group.
ERC: 40.3% (26,943 of 66,856))
TOL: 59.7% (39,913 of 66,856).
Successful VBAC: 61.4% (24,024 of 66,856)
VBAC in all women with previous cesarean: 35.9%
A hospital that had at least a 60% TOL rate in
women with previous cesarean was defined as having
a "high attempted VBAC rate".
Women who gave birth in a high VBAC rate hospital
(286,007 – includes women that did not have
a previous cesarean) had lower cesarean rates
(18.5%), higher VBAC rates (65.0%) and higher
rupture rates (0.088%).
Women that gave birth in a low rate hospital
(248,930) had higher cesarean rates (23.3%), lower
VBAC rates (55.6%) and lower uterine rupture rates
(0.056%).
Uterine Rupture
The study design did not allow for objective
definition of "uterine rupture".
All deliveries: uterine rupture rate was 0.07%
(392 of 536,785)
All women with prior cesarean: uterine rupture
rate was 0.43% (288 of 66,856)
ERC: uterine rupture rate was 0.28% (79 of 22,760)
TOL: uterine rupture rate was 0.53% (209 of 39,096)
Failed TOL: uterine rupture rate was 1.15% (174
of 15,072)
VBAC: uterine rupture rate was 0.15% (35 of 24,024)
Uterine rupture was 1.9 times more likely if
TOL was attempted but only 34% of the uterine
ruptures in women with a history of cesarean could
be attributed to TOL.
Maternal age was found to be a significant predictor
of uterine rupture but the authors were not able
to associate this with useful data such as number
of prior cesareans or number of previous pregnancies
to determine if age was independently important
or not.
The data did not include any information on fetal
outcome so there was no way to estimate the risk
of injury due to uterine rupture.
Conclusion from the study
"…in this ethnically diverse, population-based
study, the uterine rupture rate for women attempting
a trial of labor was 0.53%. This corroborates
the relative safety of VBAC, with respect to uterine
rupture, that has been demonstrated in smaller,
institutionally-based samples."
Study 4
"Delivery After Previous Cesarean: A
Risk Evaluation" Rageth JC, Juzi C, Grossenbacher,
H. Obstet and Gynecol 93: 332-337, March, 1999.
The data was collected from questionnaires that
were used to collect information for quality-control
purposes, in 40% of the deliveries in Switzerland,
from 1983 through 1996. All participants in the
study had at least one previous birth to the birth
recorded in this data set.
Women with a previous cesarean: 11.37% (29,046
out of 255,453).
TOL: 60.64% (17,613 of 29,046).
ERC: 39.36% (11,433 of 29,046).
Spontaneous onset of labor: 86.04% (15,154 of
17,613)
SOOL (spontaneous onset of labor) vaginal births:
75.06% (11,374 out of 15,154)
Induction TOL: 13.9% (2459 out of 17,613)
Induction vaginal births: 65.56% (1612 out of
2459)
Uterine Rupture
ERC: uterine rupture rate was 0.19%. (22 out
of 11,433)
TOL: uterine rupture rate was 0.39% (70 out of
17,613)
Induced TOL: uterine rupture rate was 0.65%
This difference was found to be statistically
significant.
41.43% (29 of 70) of the TOL uterine ruptures
were augmented labors.
35.80% of the TOL with no ruptures were augmented.
This difference was not found to be statistically
significant.
Maternal Complications
Women in the TOL group were statistically significantly
less likely to need a hysterectomy than women
in the ERC group (0.16% vs. 0.45%)
Women in the TOL group were statistically significantly
less likely to suffer from fever (1.5% vs. 2.29%)
Women in the TOL group were statistically significantly
less likely to have thromboembolic complications
(0.22% vs. 0.43%)
Women with a prior cesarean were 1.87 times more
likely to have a placental abruption during pregnancy
and 1.49 times more likely during labor.
Fetal Deaths and Complications
43 total fetal deaths (not associated with prematurity
or birth defects).
ERC: 0.09% (10 of 11,433 or 0.09%)
TOL: 0.19% (33 of 17,613)
This difference was slightly statistically significant.
TOL: risk of baby dying due to rupture was 0.03%
(5 of 17,613)
ERC: risk of baby dying due to rupture is 0.009%
(1of 11,433)
VBAC: babies transferred for further medical
treatment was 5.08%.
Unsuccessful TOL: babies transferred for further
medical treatment was 8.97%.
ERC: babies transferred for further medical treatment
8.30%.
Other findings:
Epidural anesthesia was associated with a higher
risk of rupture but this might be associated with
higher epidural use during induction, or other
known risk factors.
Cephalopelvic disproportion (CPD) and macrosomia
were not associated with higher rates of uterine
rupture.
Conclusion from the Study:
"Our data show that a trial of labor after
previous cesarean is safe and can be recommended
in the majority of cases."
Closing Comments
All of the studies were based on data collected
off of summary paperwork (insurance billing, birth
certificates, survey forms, other published studies),
completed by many different individuals. Other
studies have shown that the error rate in how
particular medical events (such as uterine rupture
or maternal hemorrhage) are recorded is quite
high in this type of analysis. Unless the study
authors review the actual medical chart of each
individual patient, there is the very real probability
that the data used in the study is inaccurate.
Only one of these studies (number 4) made any
attempt to determine if augmentation of labor
had an effect on rupture rates. While they concluded
that it did not, the method they used to draw
that conclusion may not have had the statistical
power to show significance.
Only one study (number 1) looked at only women
with a history of 1 prior cesarean birth and no
other births. Multiple cesareans and previous
vaginal births are known to have an affect on
a number of complications (e.g. uterine rupture
rate, placenta previa rates).
There was no information available in any of
the studies about specific characteristics of
women in the induced labor groups – cervical
readiness (Bishop’s score) may be an important
factor.
Only one study looked at epidural use (study
4) and concluded it was a risk factor for uterine
rupture, but not one that could be proven to be
independent of other risk factors. There was no
analysis of the use of other drugs during labor,
nor was there any analysis of how the women labored
(for example, confined to bed with electronic
fetal monitoring or with artificial rupture of
membranes early in the course of the labor).
The fear that is most often played upon when
a woman is being "informed" about the
risks of VBAC is the death of her baby due to
uterine rupture. It is obvious from all of these
studies that the risk of this particular outcome
is very low in the TOL groups. It is also obvious
that ERC is not a guarantee that a rupture will
not occur, nor is it a guarantee that a baby will
not die. Hopefully this information will put all
of the risks associated with VBAC vs. ERC in some
perspective.
Once again, it bears mentioning that there are
no published studies looking specifically at complication
rates in completely unmedicated, "natural"
VBACs vs. ERC or a medically managed VBAC. There
are certainly no published studies looking at
complication rates in out of hospital VBACs. Many
people assume that complication rates in the "natural"
VBAC would be lower than in any other birth –
the fact that induction is a factor in uterine
rupture and that epidural use might be, is at
least supportive of this assumption. Until data
on out of hospital VBACs is published, this must
remain an assumption.
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