Induction of labor after one previous Cesarean section in women with an unfavorable cervix: A retrospective cohort study
Induction of labor after one previous Cesarean section in women with an unfavorable cervix: A retrospective cohort study
Tove Wallstrom 1 2
Jenny Bjorklund 1 2
Joanna Frykman 1 2
Hans Jarnbert-Pettersson 1 2
Helena Akerud 2
Elisabeth Darj 0 2
Kristina Gemzell-Danielsson 2
Eva Wiberg-Itzel 1 2
0 Department of Public Health and Nursing, NTNU, Norwegian University of Science and Technology , Oslo , Norway , 4 Department of Women's and Children's Health, Karolinska Institutet, Karolinska University Hospital , Stockholm , Sweden
1 Department of Clinical Science and Education Karolinska Institute, Women's Clinic, Sodersjukhuset, Sweden, 2 Department of Immunology , Genetics and Pathology , Uppsala University , Uppsala , Sweden
2 Editor: Ricardo Queiroz Gurgel, Federal University of Sergipe , BRAZIL
Uterine rupture is a well-known but unusual complication in vaginal deliveries with a Cesarean section in the history. The risk of uterine rupture is at least two-fold when labor is induced. In Sweden, women are allowed to deliver vaginally after one previous Cesarean section, regardless if labor starts spontaneously or is induced. The aim of the study is to compare the proportion of uterine ruptures between the three methods (balloon catheter, Minprostin® and Cytotec®) for induction of labor in women with an unfavorable cervix and one previous Cesarean section.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
Funding: The authors received no specific funding
for this work.
Competing interests: The authors declared that no
competing interests exist.
Material and methods
Retrospective cohort study of all women with one previous Cesarean section and induction
of labor with an unfavorable cervix at the four largest clinics in Stockholm during 2012±
2015. Inclusion criteria: Women with a previous Cesarean section and induction of labor
with a viable fetus, cephalic presentation, singleton, at
34 w, (n = 910).
3.0% (27/910) of the women with induction of labor had a uterine rupture, 91% of them had
no previous vaginal delivery. The proportion of uterine ruptures was 2.0% (6/295) with orally
administrated Cytotec®, 2.1% (7/335) with balloon catheter and 5.0% (14/ 281) when
Minprostin® was used.
No difference in the proportion of uterine ruptures was shown when orally administrated
Cytotec® and balloon catheter were compared (p = 0.64). Orally administrated Cytotec®
and balloon catheter give a high success rate of vaginal deliveries (almost 70%) despite an
Cesarean section (CS) is a common procedure in obstetric care, with 25±50% of all deliveries
worldwide ending with a CS[
]. A previous CS is known to be one of the strongest risk factors
for uterine rupture (UR) in the following delivery [2±4]. The incidence of UR among women
with one previous CS is assumed to be 0.5±0.9% [
2, 3, 5
], compared to 0.2 ½ in women
without any history of CS [
]. Factors such as induction of labor (IOL), fetus large for gestational
age (> 4000g), labor dystocia, maternal height 160 cm and age > 35years are all known to
increase the risk of a UR [4±7]. Although in women with a previous CS the overall incidence
of UR is low. Women with a vaginal delivery before or after the primary CS are more likely to
have a successful vaginal delivery even after a previous CS in the subsequent labor [8±11].
IOL after a previous CS is a controversial intervention. The proportion of UR in the Trial of
Labor after Cesarean section group (TOLAC) with IOL is reported as high as 1.4% and an
association with the use of vaginal prostaglandins has been shown [2, 3, 12±15].
Misoprostol (Cytotec1) is a prostaglandin, used for IOL worldwide. Since 2012, Cytotec1,
administrated as an oral solution, is the recommended method for IOL in Sweden. From the
onset, this was also used among women with one previous CS.
At Sodersjukhuset in Stockholm the proportion of subsequent CS decreased from on
average 40.5% before the use of oral solution of Cytotec1 to 23.0% afterwards. Before Cytotec1,
Minprostin1 1mg and balloon catheter were used as primary methods for IOL in this group
of women. There was no increase in maternal or fetal complications after the change of
method (only statistics from medical records is available, no published data.)
In Sweden, IOL is recommended after one previous CS. After 2016 Cytotec1 was
discouraged in the Swedish guidelines for IOL after one previous CS, even though scientific
knowledge was limited and based only on small studies where only vaginal and not oral
administrated solution of Cytotec1 was used [1, 16±18].
No prostaglandins at all were recommended as they were considered to increase the risk of
UR, compared to balloon catheter[
The Primary aim of this study was to compare the proportion of UR between the three
methods (balloon catheter, Minprostin1 and Cytotec1) for IOL in women with an unfavorable
cervix and one previous CS. The secondary endpoint was to study the delivery outcomes such
as mode of delivery and the outcome of the new-born in the TOLAC group.
This was a retrospective cohort study of all women with one previous CS, unfavorable cervix,
and IOL at the four largest hospitals in Stockholm: Danderyd's hospital (no 1), Karolinska
Hospital in Huddinge (no 2), Karolinska Hospital in Solna (no 3), and Sodersjukhuset (no 4)
during the period from 2012 to 2015 (n = 910). Data from all induced deliveries at these four
delivery wards during the actual study period were collected from the Obstetrix database (the
main used medical record system in Sweden) All personal data were encoded, so that
individuals could not be identified in the analysis.
Inclusion criteria for the study were women with one previous CS and IOL. All women
included had a viable fetus in cephalic presentation, singleton, at gestational age of 34 weeks.
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Different types of medical preparations such as vaginal dinoproston (Minprostin1, a
vaginal gel, Pfizer, NY, USA, or Propess1, an insert with slow-release of prostaglandin E2,
Ferring, Malmo, Sweden) or mechanical methods (balloon catheters, Bard1/Rusch1, Cook
Medical, USA) were used previously for IOL as primary methods in the case of an
unfavourable cervix (Bishop score (BS) 5). From 2012, Cytotec1 was also administrated as an oral
solution for the same indication at the included hospitals.
In the Cytotec1 group, Cytotec1 was prepared as an oral solution, one tablet of 200 μg
Cytotec1 was dissolved in 20 ml of water. The solution thus held 10 μg of Cytotec1/ml. This
method of administration has been tested by the Swedish Institute of Pharmacology [
approved to be accurate in terms of correct dosage. A dose of 2.5 ml / 25 μg of Cytotec1 were
administered orally to the women every two hours until frequent painful contractions were
obtained. The dose could be repeated up to eight times if necessary (maximum 200ug in 24h).
When ripening of the cervix had been achieved (BS 5), amniotomy and oxytocin were used
to support uterine contractions.
In the Minprostin1 group, 1 or 2 mg of Minprostin1 was given vaginally. The progress of
induction was evaluated by a vaginal examination every six hours. In the case of a still
unfavourable cervix, additional doses were administered, up to a total of three doses (6 mg). When
ripening of the cervix had been achieved (BS 5), amniotomy and oxytocin were used to
support labor contractions.
In the balloon group, mechanical IOL was performed with a balloon catheter (Bard1). The
balloon was inserted into the cervix beyond the internal os and the bulb inflated with 50 ml of
sterile water. The midwife stretches the catheter every 30 minutes. The balloon could be used
for a maximum of 10h. At a cervical dilation of at least 3 cm, the balloon was expelled and the
induction was followed by amniotomy and oxytocin.
No additional method was used after the primary method of induction in 84.1% (248/295)
deliveries in the Cytotec1 group, in 80.4% (226/281) in the Minprostin1 group and in 97.1%
(326/335) in the balloon group. As most of the women (minimum 80%) received only one
method of induction, we consider it appropriate to use the first method of induction as the
main method for calculation. 37.5% (105/280) of the women in the Minprostin1 group
received two doses of Minprostin1 and 9.3% (26/280) received a third dose.
A total UR was defined as a complete separation of all layers of the uterine wall, including
myometrium and the serosa. A dehiscence was defined as a separation of the muscular layers,
with intact serosa[
IOL in an unfavorable cervix strives to reach amniotomy. Amniotomy itself is therefore not
considered as an additional method of IOL in this study. Amniotomy followed by stimulation
with oxytocin were used in deliveries with a favourable cervix (BS 6), and oxytocin only, was
used primarily in cases with ruptured membranes and a favourable cervix.
Immediately after birth, before the new-born first cry, an arterial and a venous cord blood
sample were drawn from a segment of the cord without clamping. Arterial pH and base deficit
(BD) were analyzed within a few minutes with a point-of-care device (ABL 800 Bayer1),
available in the delivery wards. This is a routine clinical procedure in all the delivery wards in
One-way ANOVA (ANalysis Of Variance) was used to compare mean values, and the
Chisquare test to compare the proportions, between the different methods of induction. In this
study the association between the proportion of UR (primary outcome) and method of
induction was analysed, and logistic regression was used to adjust this association with respect to
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other risk factors for UR. We adjusted for possible explanatory variables such as maternal age
(<30 years or >30 years), previous vaginal delivery (yes or no), gestational age (<41+0 weeks
or 41+0 weeks), delivery unit/hospital (no 1±4), indication for induction (Premature
Rupture Of Membrane (PROM), Postdate ( 41 weeks), maternal, fetal, non-medical, prolonged
latent phase), BS ( 5 or >5), method of induction (Cytotec1, Minprostin1, balloon),
delivery time ( 12h, >12 24h, >24h), time of augmentation with oxytocin (<10h, >10h) and
type of CS (Elective Cesarean section (ES), Acute Cesarean section (AS)). First, we calculated
the crude (unadjusted) associations of each possible explanatory variable and UR. Second, we
used multivariable models to study the adjusted associations with respect to the variables
above. Finally, to study whether the method of induction differed in any subgroup with
respect to the levels of variables, we added an interaction to the adjusted model between the
method of induction and each of the possible explanatory variable, one at a time. Model fit was
judged based on the Hosmer and Lemeshow Goodness-of-fit test, if p>0.05 the model fit was
acceptable. The associations are presented as odds ratios (OR) with 95% confidence intervals
No pre-power calculation was done since the study was register based and the rationale for
the number of observations therefore was to use all available data. However, we performed a
post-hoc calculation to see how differences in our primary outcome (rupture (yes/no)) that the
study was dimensioned to detect with the actual number of individuals. We would have 80%
power (5% significance level, two-sided) to detect a difference in the proportion with uterine
rupture of 2.0% vs 7.3% between the groups of women who received Cytotec1 (n = 295) and
Minprostin1 (n = 280). A p-value <0.05 was considered statistically significant. Statistical
analyses were performed using SPSS 23.0 (SPSS Inc., Chicago, IL.).
The study was approved by the regional ethics committee (Karolinska Institute, file record:
2016/1494). The study complies with the World Medical Association Helsinki Declaration
regarding ethical conduct of research involving human subjects.
During study time 87,774 deliveries occurred at the four largest delivery wards in Stockholm.
There were 11.3% (9,941/87,774) women that had a previous CS, and almost every second of
them (48.4%) were planned for an ES before onset of labor. After exclusion of pregnancies
<34 gestational weeks, multiples and IUFD, 4,997 deliveries remained. There were 23.0%
(1,150/4,997) of the remaining deliveries that went for IOL. The majority, 79% (910/1,150) of
them had an unfavorable cervix with a BS 5, and a balloon catheter, Minprostin1 or an oral
solution of Cytotec1 were used for induction of labor (Fig 1).
Table 1, describes baseline data from all the induced deliveries with an unfavorable cervix
with respect to the method of induction. No statistically significant difference was found
between the three groups of inductions except maternal age, where women in the balloon
group were younger (32.5 years) compared to the Minprostin1 group (33.4 years) and
Cytotec1 group ((34.1 years) p<0.01). There was a significant difference between methods of
choice between the four hospitals in Stockholm (p<0.01). Cytotec1 was the method of choice
at hospital no 4 (89.5%), Minprostin1 at hospital no 1 and no 2 (44.6% vs 37.9%), and a
balloon catheter primary at hospital no 3 (47.8%, Table 1).
A statistically significant difference in BS at the time of induction was found between the
three groups, with highest BS (4) in the balloon group and the lowest (2.4) score in the
Minprostin1 group (Table 1.).
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Fig 1. Flowchart.
There was a significant difference in the indication for induction (p<0.01). The most
common reason overall was post-dated pregnancies ( 41w of gestation, 24.7%) followed by
PROM (21.4%), fetal reason (19.5%), non-medical reason (15.1%), maternal reason (14.1%)
and prolonged latent phase (5.7%, Table 1.).
A significant difference (p<0.01) in time from the start of induction to delivery was found
among the deliveries included. The shortest time was found in the balloon group 14.3 h (1.2±
43.1h) and longest in the Minprostin1 group 21.7h (2.1±62.1h, Table 2.). Even a statistically
significant difference in the use of oxytocin was found. The highest proportion and longest
time of stimulation were found in the balloon group (88.4% and 8.5 h), and the lowest
proportion and shortest time of stimulation were found in the Cytotec1 group, (56.9% and 6.9 h,
p<0.01, Table 2.).
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The mode of delivery varied between the three different groups presented. CS was most
common in the Minprostin1 group (42.9%), compared to almost similar frequencies in the
balloon (31.0%) and the Cytotec1 (30.8%) groups (Table 2).
Three percent (27/910) of the deliveries included had a UR discovered during or after
delivery. A difference among deliveries with UR was shown according to the proportion of a
previous vaginal delivery. The majority (91%) of the women with UR had no history of vaginal
delivery, compared to 69% of the women with no UR (p<0.01).
In 22.2% (6/27) the UR was considered as total (at least a part of the fetus in the abdominal
cavity), and in 33.3% (9/27) a dehiscence was found. No difference was identified among the
groups according to the size of the rupture (5< or 5cm), 22% (6/27) had a UR <5cm and the
same proportion had a UR >5 cm. No statistically significant difference was found according
to the method of induction and type of rupture (Table 2).
When studying the method of induction, it can be concluded that 5.0% (14/280) of the UR
occurred in the group where Minprostin1 was used, 2.1% in the balloon group (7/335) and 2.0%
(6/295) in the group with orally administrated Cytotec1 (6/295). The remaining cases were
found in the group where amniotomy was used as the primary method of IOL (2/190, 1.1%).
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No statistical difference was found when considering the indications for IOL. There was
neither a statistical difference between those women who had a UR and those who did not,
regarding the status of the cervix at the beginning of the induction (Table 3).
No previous vaginal delivery was the strongest risk factor in this study for having a UR
during labor (OR 4.1; 95% CI; 1. -17.3, Table 3) after one previous CS, but after adjustment for the
other possible risk factors for UR the result was no longer statistically significant (aOR 2.8;
95% CI; 0.6±12.6). Prolonged labor >24 h was associated with an increased risk for having a
UR (OR 3.9; 95% CI; 1.2±12). After adjustment for the other factors, the result was no longer
significant (aOR 3.4 95% CI; 0.9±13.0).
Induction of labor with Minprostin1 was associated with an increased risk for having a
UR (OR 2.5.; 95% CI; 1.0±6.2, Table 3.). After adjustment for other possible risk factors for UR
in Table 3, the result was no longer significant (aOR 1.2; 95% CI; 0.4±3.9).
No significant interactions were found (p-values between 0.27 and 1.0). The Hosmer and
Lemeshow test and Goodness of fit test were equal to p = 0.50 for the adjusted model (n = 910).
The proportion of low Apgar score <7 after 5 min was statistically significant (11.5% vs
0.8%), low pH <7.10 (20.5% vs 4.4%) and post-partum hemorrhage (PPH)>1000 ml (30.8%
vs 11.2%) between UR and non-UR groups. The proportion of CS was statically significantly
higher in the UR group (79.5%) than in the non-UR group (26.8%).
Our main finding in this project is that the proportion of UR was equal when a balloon
catheter was used compared to the group with orally administrated Cytotec1 (2.1 vs. 2.0%,
Time from induction to delivery (h)
Frequency of oxytocin drip (n = 637)
Time of Oxytocin drip(h)
Frequency of UR (n = 27)
Type of UR (n = 27)
-Dehiscence (n = 9)
<5cm (n = 6)
.>5cm (n = 6)
Total rupture (n = 6)
Way of delivery (%)
Vaginal (n = 595)
CS (n = 315)
>1000ml (n = 115)
>1500ml (n = 56)
Fetal weight (g)
Fetal height (cm)
Fetal head circumference (cm)
Apgar <7, 5'
pH < 7.10 (n = 41)
Missing (n = 222)
Fetal death (n = 0)
Cytotec1 (n = 295)
Minprostin1 (n = 281)
p = 1.0). The success rate of vaginal delivery after one previous CS (VBAC) in women with
IOL is very high, almost 70% with both balloon catheter and oral solution of Cytotec1,
regardless of BS.
PLOS ONE | https://doi.org/10.1371/journal.pone.0200024
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Strengths and limitations
The strengths of this project are that there are no other studies where oral solution of
Cytotec1 administrated in this way is presented among women with one previous CS. Even
though this is a retrospective study, a careful study was made of the medical records of all
women included, which make the results even more reliable.
A limitation of this project is that the study is not a randomized controlled trial, which
would have been desirable. Although the study population is large, the main outcome -UR- is
unusual, which means that even larger populations need to be studied. Another question is
whether randomization in this group would be perceived as ethical, when there is an increased
risk for UR with IOL in the group of women with a previous CS?
Another limitation in the study is that the balloon group had a significant higher BS (4)
compared to Cytotec1 (2.9) and Minprostin1 (2.4, (p <0.001)) and therefor probably had
the shortest time interval from IOL to delivery, 14.3 h (1.2±43.1h). The longest time were
found in the Minprostin1 group 21.7h (2.1±62.1h) where the BS was lowest. However, the
rate of UR in the balloon group was similar compared to the Cytotec1 group despite the
shorter delivery time and more favorable cervix.
Whether prostaglandins given in different forms increase the risk of UR compared to other
methods of induction is a question that is still under discussion [
]. According to previous
studies, misoprostol administrated vaginally will increase the risk of UR [22±24]. Misoprostol
in all forms has therefore been discouraged in various guidelines on labor induction in women
with previous CS even though the scientific knowledge is limited [
17, 18, 25
]. However, the
evidence is unclear and based on only small studies where only vaginally administrated
misoprostol has been studied.
A solution of Cytotec1 administrated orally was introduced at hospital no 4 in Stockholm
at 2012 also in IOL among women with one previous CS. This was after the method had been
used with very good results in the group of IOL among women without a uterine scar. The
other hospitals in Stockholm introduced the method after some tests had been made by the
Swedish Institute of Pharmacology [
]. The occurrence of hyper-stimulation was low (1%) in
the Cytotec1 group compared to the Minprostin1 group where at least 15% experienced
hyper-stimulation at the clinic (no published data available). Our current results are analogue
to Gemzell-Danielsson et al [
], How et al  and Aronsson et al [
] who concluded
that orally administrated misoprostol actually caused less uterine hyper-stimulation than
vaginal or sublingual administration. What was notable was that the proportion of CS decreased
significantly in the group of women with a previous CS after IOL when an oral solution of
Cytotec1 was introduced at the clinic, without increasing complications.
Our study shows that IOL with oral solution of Cytotec1 after one previous CS is a safe
and effective method well comparable with the use of a balloon catheter, despite a more
unfavorable status of the cervix. Oral solution of Cytotec1 gives a significantly increased rate of
VBAC compared to Minprostin1 (69.2% vs 57.2%, p = 0.02) and the same successful rate as
balloon catheter (69.2 vs 69.0%) even though the primary BS was different in the two groups.
In our opinion, an oral solution of Cytotec1 is a good alternative when IOL is needed in
women with one previous CS and an unfavorable status of the cervix.
The increased risk of UR may be related to characteristics of the woman herself who
receives prostaglandins rather than the drug itself; as for an example, women who receive
prostaglandins are much more likely to have an unfavorable cervix than women induced with
oxytocin or who enter labor spontaneously[
]. According to Harper et al [
], IOL is not
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associated with an increased risk of UR when duration of labor is considered. It is important
to have a normal progress of labor among women with a previous CS, and all arrested
deliveries should be avoided in this group. If labor is extended, a CS should be considered at an early
state of labor, to avoid traumatic labor outcomes as far as possible. In our opinion it is highly
important to have a various selection of methods for IOL after a previous CS especially when
the cervix is unfavorable.
An important question raised in this project is whether we should continue to induce
women after one previous CS. Is it justifiable that as many as 3% rupture during ongoing
labor? We know that a UR during labor is often a serious event, for the woman, the fetus and
for the staff in charge. Repeat CS should on the other hand be avoided if possible as they are
associated with complications, but the most important criterion is to avoid the very first CS. If
it is considered justifiable, the challenge might be to identify women suitable for induction,
and to make the delivery as good and risk-free as possible for both the woman and her unborn
Our final conclusions are that an orally administrated solution of Cytotec1 is a good method
for IOL even among women with one previous CS. Most UR in this study occurred when
Minprostin1 was used (5.0%), the risk is more than two-fold compared to Cytotec1 and balloon
catheter. No difference in the proportion of UR was shown when orally administrated
Cytotec1 and balloon catheter were compared (p = 0.64). Orally administrated Cytotec1 as well
as balloon catheter give a high success rate of VBAC (almost 70%) despite an unfavorable
cervix. Our hope is that Cytotec1 will be used, with caution, as one of many methods for IOL in
S1 Dataset. Data uterine ruptures study 4.
We wish to thank Marilyn Hedges for language editing.
Conceptualization: Tove Wallstrom, Helena Akerud, Elisabeth Darj, Kristina
Danielsson, Eva Wiberg-Itzel.
Data curation: Tove Wallstrom, Jenny Bjorklund, Joanna Frykman, Hans Jarnbert-Pettersson,
Formal analysis: Tove Wallstrom, Hans Jarnbert-Pettersson, Eva Wiberg-Itzel.
Methodology: Tove Wallstrom, Eva Wiberg-Itzel.
Supervision: Eva Wiberg-Itzel.
Writing ± original draft: Tove Wallstrom.
Writing ± review & editing: Tove Wallstrom, Jenny Bjorklund, Joanna Frykman, Helena
Akerud, Elisabeth Darj, Kristina Gemzell-Danielsson, Eva Wiberg-Itzel.
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